Introduction

My UFC prediction model has maintained profitable performance for years despite having poorly calibrated probability estimates. While the model excels at binary classification (picking winners), its confidence scores don't align well with real-world win frequencies—a classic case of good accuracy, bad calibration.

This never bothered me much since the model was profitable, but I decided to experiment with post-hoc calibration methods to see if I could improve probability estimates without hurting classification performance. This post documents those experiments: the methods I tested, why most failed with limited data, and the modest improvements I eventually achieved with Platt scaling.

What is Model Calibration?

Model calibration refers to how well a model's predicted probabilities align with actual observed frequencies. A perfectly calibrated model should be correct 70% of the time when it predicts a 70% probability, 80% of the time when it predicts 80%, and so on.

Consider this example: if your model predicts 100 fights at 60% confidence, and the favored fighter wins 60 of those fights, your model is well-calibrated at that confidence level. However, if the favored fighter wins 75 times, your model is under-confident and poorly calibrated.

from sklearn.calibration import calibration_curve
import matplotlib.pyplot as plt

# Example: plotting calibration curve
fraction_pos, mean_pred = calibration_curve(y_true, y_prob, n_bins=10)
plt.plot([0, 1], [0, 1], 'k--', label='Perfect calibration')
plt.plot(mean_pred, fraction_pos, 's-', label='Model')
plt.xlabel('Mean Predicted Probability')
plt.ylabel('Fraction of Positives')

The Calibration vs. Accuracy Paradox

One of the most counterintuitive aspects of calibration is that improving probability estimates can sometimes hurt classification accuracy. This happens because calibration optimizes for probability-based metrics like log-loss and Brier score, while accuracy only cares about the binary decision boundary at 50%.

Why This Happens

Consider a model that consistently predicts 65% when the true probability is 60%. This model might achieve higher accuracy by being overconfident (correctly picking the winner more often due to increased confidence), but it's poorly calibrated. When calibrated, the model's predictions become more conservative, potentially crossing the 50% decision boundary in some cases and reducing accuracy.

In my UFC model, this manifested as:

Original Model Performance:
  Accuracy:    0.7098
  Log Loss:    0.6032
  Brier Score: 0.2075

Calibrated Model Performance:  
  Accuracy:    0.7098 (unchanged)
  Log Loss:    0.5979 (improved by 0.0053)
  Brier Score: 0.2056 (improved by 0.0019)

The accuracy remained stable while probability-based metrics improved significantly but that isn't true for all calibration methods and isn't even necessarily true 100% of the time for the method that actually worked.

The Small Sample Size Challenge

My dataset contains approximately 2,400 UFC fights over 10 years after extensive filtering:

def filter_fights(df, threshold, date='2015-01-01', include_split_dec=False):
    """
    Filter fights based on:
      - Binary results (y_true in [0, 1])
      - Both fighters must have had at least num_fights previous fights
      - Removing unwanted fight methods (DQ, split decisions, etc.)
      - Fights from 2015 onward
    """
    # Remove unwanted methods
    if include_split_dec:
        unwanted_methods = ['dq', 'other', 'overturned']
    else:
        unwanted_methods = ['dq', 'other', 'decision - split', 'decision - majority', 'overturned']
    
    # Filter to only binary results and recent fights
    df = df[df['y_true'].isin([0, 1])].copy()
    df = df[df['event_date'] >= pd.Timestamp(date)]
    
    return df

This small sample size created significant challenges for calibration, particularly with isotonic regression which requires sufficient data points across the probability spectrum.

Isotonic Regression: The First Attempt

Isotonic regression is a non-parametric calibration method that learns a monotonic mapping from predicted probabilities to calibrated probabilities. It's theoretically superior to Platt scaling as it can capture non-linear calibration relationships.

class SimpleIsotonicCalibration:
    def __init__(self, y_min=0.01, y_max=0.99):
        self.y_min = y_min
        self.y_max = y_max
        self.calibrator = None
        
    def fit(self, y_prob, y_true):
        from sklearn.isotonic import IsotonicRegression
        
        self.calibrator = IsotonicRegression(
            y_min=self.y_min,
            y_max=self.y_max,
            out_of_bounds='clip'
        )
        self.calibrator.fit(y_prob, y_true)

Isotonic Results (Disappointing)

Isotonic Calibration Results:
Should Use Calibration: False
Calibration Set Log Loss Improvement: 0.0553 # Improvement on the calibration set of data
Test Set Log Loss Improvement: 0.0125  # Worse on the unseen test set!
Test Set Brier Score Improvement: 0.0023 # Worse on the unseen test set!
Final Test Log Loss (Original): 0.5937
Final Test Log Loss (Calibrated): 0.6063

The isotonic calibration actually hurt performance on the test set despite improving calibration set metrics. This is a classic sign of overfitting due to insufficient data.

Why Isotonic Failed

1. Small sample size: With only ~240 test samples (10% of 2,400), isotonic regression had insufficient data to learn a robust monotonic mapping
2. Sparse probability regions: Some probability ranges had very few examples, leading to unreliable calibration
3. Overfitting: The flexibility of isotonic regression became a liability with limited data

I attempted several improvements:

• Ensemble approach: Multiple isotonic regressors trained on different CV folds using all the training data. This was dumb because I was just training the calibration model on fights the main model had already been trained on leading to overfitting on train, and poor results on the holdout test dataset.
• Expanded calibration set: Increased from 10% to 20% of data
• Parameter tuning: Adjusted y_min, y_max, and out_of_bounds settings

None of these approaches yielded meaningful improvements.

Platt Scaling: A Little Better

Platt scaling uses logistic regression to map uncalibrated probabilities to calibrated ones. While less flexible than isotonic regression, it's much more suitable for small datasets.

class SimplePlattCalibration:
    def __init__(self, max_iter=100, random_state=42):
        self.max_iter = max_iter
        self.random_state = random_state
        self.calibrator = None
        
    def fit(self, y_prob, y_true):
        from sklearn.linear_model import LogisticRegression
        
        # Reshape probabilities for sklearn (needs 2D input)
        y_prob_reshaped = y_prob.reshape(-1, 1)
        
        self.calibrator = LogisticRegression(
            max_iter=self.max_iter,
            random_state=self.random_state,
            solver='lbfgs'
        )
        self.calibrator.fit(y_prob_reshaped, y_true)

Implementation in Training Pipeline

The calibration was integrated into the training pipeline using scikit-learn's CalibratedClassifierCV:

# Three-way split for proper calibration validation
(X_train, y_train), (X_cal, y_cal), (X_test, y_test) = split_data_three_way(
    X, y, train_size=0.775, val_size=0.125
)

# Wrap AutoGluon predictor for sklearn compatibility
autogluon_wrapper = AutoGluonWrapper(predictor, feature_columns=X_train.columns.tolist())

# Create calibrated classifier using holdout method
calibrated_clf = CalibratedClassifierCV(
    estimator=autogluon_wrapper,
    method='sigmoid',  # Platt scaling
    cv="prefit",       # Use prefit since AutoGluon is already trained
    ensemble=False     # Use single calibrator since we have proper split
)

# Fit calibrator on holdout calibration set
calibrated_clf.fit(X_cal_clean, y_cal)

Platt Scaling Results (Success!)

Calibration Results (sigmoid):
Should Use Calibration: True
Calibration Set Log Loss Improvement: 0.0098
Test Set Log Loss Improvement: 0.0107
Test Set Brier Score Improvement: 0.0043
Test Set ECE Improvement: 0.0174
Final Test Log Loss (Original): 0.5948
Final Test Log Loss (Calibrated): 0.5841

The improvement of 0.0107 in log-loss on the holdout test set of data represents a meaningful, if small, gain in probability accuracy.

Profitability Impact Analysis

While the statistical improvements were modest, I wanted to examine whether calibration affected betting profitability. Here's the cumulative profit comparison between the original and calibrated models on the test set:

The results show modest but consistent improvements across most betting strategies. The core strategy (ai_all_picks_closing) improved from 13.26% to 13.60% ROI, while the seven-day advance strategy increased from 14.98% to 15.30% ROI. Notably, win percentages remained identical at 70.70% which is interesting because some picks do change based on the calibration process.

Interestingly, underdog-focused strategies saw slight decreases in ROI (35.31% to 34.97% for closing odds) and slightly improved favorite win percentages (70.70% to 70.80%), suggesting the calibration process may have made the model slightly more conservative on high-value underdog picks. Meanwhile, the poorly performing +EV on ANY fighter (regardless of AI pick) strategies remained unprofitable in both versions but dramatically improved in the calibrated version showing the calibration process working in action. The AI-picked +EV strategy was basically the same though which tells me I need more profit testing on where the +EV threshold is, like +5% win chance? +10% win chance? When do we bet against the AI pick? Like last event Kevin Holland was picked by AI at -180 or something yet Vegas had him at -500. What's the threshold to pick against the AI? IDK yet but I'll go test it out. This is the most pressing question when we're talking about betting strategy.

However, it's crucial to note that ROI is a moving target—betting markets evolve, line movement varies, and small sample sizes can significantly impact results. These profit tests represent performance on a specific test set and shouldn't be viewed as guaranteed future returns. The real value of calibration lies in more reliable probability estimates for bet sizing and strategy decisions rather than raw profit maximization.

Model Performance Analysis

Here's how the calibrated model performed against Vegas odds across all unfiltered fights in the past 1.5 years (meaning we include split decisions, and DQ's, and whatnot which aren't included in the model training):

{
  "vegas_odds_performance": {
    "accuracy": 0.700,
    "log_loss": 0.563,
    "brier_score": 0.194
  },
  "mma_ai_performance": {
    "accuracy": 0.710,
    "log_loss": 0.603,
    "brier_score": 0.208
  },
  "mma_ai_performance_calibrated": {
    "accuracy": 0.710,
    "log_loss": 0.598,  # Improved
    "brier_score": 0.206  # Improved
  }
}

The calibrated model maintains identical accuracy while providing more reliable probability estimates.

The Calibration Curve Analysis

The most telling evidence comes from the calibration curve itself. My uncalibrated model exhibited classic miscalibration patterns:

• Underconfident in 50-60% range: When the model predicted 55%, fighters actually won ~60% of the time
• Overconfident in 40-50% range: When the model predicted 45%, fighters won closer to 40% of the time

def plot_calibration_curve(self, n_bins=10, include_all_fights: bool = False):
    # Get calibrated predictions if calibrator is available
    y_prob_calibrated = None
    if self.calibrator is not None:
        y_prob_calibrated = self.calibrator.predict_proba(test_data_clean)[:, 1]
    
    # Calculate calibration curves
    prob_true_model, prob_pred_model = calibration_curve(self.y_test, y_prob_model, n_bins=n_bins)
    if y_prob_calibrated is not None:
        prob_true_calibrated, prob_pred_calibrated = calibration_curve(
            self.y_test, y_prob_calibrated, n_bins=n_bins
        )
    
    # Plot results
    plt.plot([0, 1], [0, 1], 'k--', label='Perfect Calibration')
    plt.plot(prob_pred_model, prob_true_model, 's-', label='Model (Original)')
    if y_prob_calibrated is not None:
        plt.plot(prob_pred_calibrated, prob_true_calibrated, '^-', 
                label='Model Calibrated', alpha=0.8)

The Odds Inclusion Paradox

An interesting discovery was the relationship between including betting odds and calibration. In previous experiments 1-2 years ago, calibration consistently hurt performance. The key difference was I was including Vegas odds as features.

With Odds (Historical)

• Pros: Exceptional calibration, higher accuracy (~73-74%)
• Cons: Model HEAVILY favored odds over other features, struggled with underdog picks, -6% lower ROI against all model picks

Without Odds (Current)

• Pros: Better underdog detection, higher betting ROI, room for calibration improvement
• Cons: Lower accuracy (~71%), requires manual calibration

This represents a fascinating tradeoff: accuracy vs. profitability. The model without odds hits significantly more profitable underdog picks, even though its raw accuracy is lower.

Why Calibration Matters for Bettors

While calibration may not be necessary for a profitable model (mine was already profitable before calibration), it provides crucial benefits for bet sizing and strategy:

Kelly Criterion Application

With well-calibrated probabilities, bettors can use the Kelly Criterion more effectively:

def kelly_bet_size(prob, odds, bankroll):
    """Calculate optimal bet size using Kelly Criterion"""
    decimal_odds = american_to_decimal(odds)
    edge = prob * decimal_odds - 1
    if edge <= 0:
        return 0
    kelly_fraction = edge / (decimal_odds - 1)
    return min(kelly_fraction * bankroll, bankroll * 0.1)  # Cap at 10%

I experimented with fractional kelly in the past. It's promising long term, especially since the model's logloss is consistently less than .059, but the wild swings are too painful. If we got the model to be lower logloss than Vegas by including the odds in the feature set I think this is promising but will experiment more later with that.

Confidence-Based Strategies

Calibrated probabilities enable more sophisticated betting strategies:

def edge_based_betting_strategy(predictions, min_edge=0.05):
    """Select bets based on edge over Vegas odds rather than absolute confidence."""
    betting_opportunities = []
    
    for fight in predictions:
        # Get model probability and Vegas implied probability
        model_prob = fight['model_confidence']
        vegas_decimal_odds = american_to_decimal(fight['vegas_odds'])
        vegas_implied_prob = 1 / vegas_decimal_odds
        
        # Calculate edge (model probability - market probability)
        edge = model_prob - vegas_implied_prob
        
        # Only bet if we have a significant edge
        if edge >= min_edge:
            kelly_fraction = edge / (vegas_decimal_odds - 1)  # Kelly criterion
            betting_opportunities.append({
                'pick': fight['fighter_name'],
                'edge': edge,
            })
    
    return betting_opportunities

I'll probably implement something like this later on after I do more profitability backtesting with flat units.

Technical Implementation Details

The final calibration system integrates seamlessly with the existing prediction pipeline:

def _get_model_predictions(self, test_data, use_calibrated=None):
    """Get model predictions, optionally using calibrator."""
    if use_calibrated is None:
        use_calibrated = self.calibrator is not None
    
    # Get original predictions
    y_pred = self.predictor.predict(test_data)
    y_prob = self.predictor.predict_proba(test_data)
    
    # Apply calibration if available
    if use_calibrated and self.calibrator is not None:
        test_data_clean = test_data.drop(columns=['sample_weight'], errors='ignore')
        y_prob = self.calibrator.predict_proba(test_data_clean)[:, 1]
        y_pred = (y_prob > 0.5).astype(int)
    
    return y_pred, y_prob

Lessons Learned

1. Dataset size matters: Isotonic regression requires substantial data; Platt scaling works better with limited samples
2. Validation strategy is crucial: Proper train/calibration/test splits prevent overfitting
3. Calibration ≠ Accuracy: Better probabilities don't always mean better classifications
4. Feature engineering impacts calibration: Including odds improves calibration but hurts profitability
5. Domain expertise guides tradeoffs: Understanding the betting market informed the decision to exclude odds

Conclusion

While the final improvement in logloss was modest (0.0107), it represents a meaningful step toward more reliable probability estimates.

The key insight is that calibration serves different purposes depending on your goals. For pure classification accuracy, it is unnecessary. For models that are already well calibrated (like when you include the odds, or use algos that are better for calibration like Random Forest) calibrating the predictions using Platt or Isotonic harms the output.

The surprising relationship between feature inclusion (odds) and calibration highlights the complex tradeoffs in machine learning systems. Sometimes the most accurate model isn't the most profitable one, and the most calibrated model isn't the most accurate one.

For practitioners working with limited datasets, Platt scaling offers a robust path to improved calibration. The simplicity of logistic regression makes it both interpretable and reliable, even when more sophisticated methods fail.

Not at this time. I've spent so many hours investigating this in my free time. ROI is our north star, with logloss and accuracy being secondary metrics. This isn't a perfect test because the betting markets shift as time moves. For example, 2016 saw Vegas favorites win only 61% of the time. 2024 saw favorites win 70% of the time and UFC red corner is usually the betting odds favorite. So this isn't the end-all be-all conclusion, but it is absolutely the point in time conclusion.

The long and short of the massive amount of trial and error is this backtested ROI based on the last year of fights the model has never seen:

ROI Comparison: Balanced vs Unbalanced Training

ROI of balanced 50/50 fighter1 win/lose:

ROI of unbalanced 59/41 fighter1 (UFC assigned red corner) win/lose:

Based on how I do feature engineering and model tuning, balancing the fighters' win rate before training the model is terrible. If I do some various feature and model tuning I can see the balanced model start to perform closer to the unbalanced model but on average it is basically always lower ROI. I have interrogated my code a thousand times with Claude4 Opus and Gemini 2.5 Pro to try to suss out any logical errors and I cannot find any.

Why Does Balanced Training Destroy Performance?

*Begin speculation*

Distribution shift between training and inference creates systematic probability miscalibration. When you balance the dataset to 50/50, you're teaching the model that P(fighter1_wins) = 0.5 across all feature combinations. But in reality, fighter1 (red corner) wins ~60% of the time because the UFC systematically assigns the red corner to champions in title fights and generally more experienced/favored fighters in regular bouts.

The calibration mismatch:

• Training: Model learns P(fighter1_wins | features) where the base rate is artificially 0.5
• Inference: Model predicts on data where the true base rate is 0.6

This specifically destroys betting ROI because:

• Systematic underestimation of favorites: When a red corner fighter should win with 70% probability, your balanced model might predict 60%, causing you to miss profitable favorite bets
• Systematic overestimation of underdogs: When a blue corner fighter should win with 30% probability, your model might predict 40%, leading to negative EV underdog bets
• Market inefficiency amplification: The higher ROI without balancing implies that the model is learning this pattern of corner bias more efficiently than the market is.

The model's probability outputs are fundamentally miscalibrated for the real world's corner assignment bias. You're essentially training a model for a balanced fantasy UFC and then applying it to the systematically biased real UFC, where corner assignments carry predictive information about fight outcomes.

Bottom line: The balanced training throws away valuable signal (red corner = usually stronger fighter) and teaches the model incorrect base rates, leading to systematically poor probability estimates that destroy betting performance.

Doesn't Calibrating the Winrate Just Create a Proxy for the Odds?

No, and here's why that concern misses the point:

The model isn't learning "red corner = bet favorite." It's learning complex feature interactions from granular performance statistics that happen to correlate with corner assignments. The red corner correlation exists because the UFC assigns corners based on ranking, championship status, and experience - the same underlying factors that drive fight outcomes.

Key distinctions:

• Betting odds reflect public perception, line movement, and bookmaker risk management
• The model analyzes actual performance metrics: strike accuracy trends, takedown defense patterns, cardio indicators, opponent-adjusted statistics, etc.
• The value comes from divergence identification based on as much statistical information as possible. The corner bias is simply real world information that the model can learn to incorporate better than average bettors.

The unbalanced training preserves the signal that corner assignments carry meaningful information about fighter quality, information that's already baked into the real-world problem you're trying to solve. Throwing away that signal artificially handicaps the model's ability to make properly calibrated predictions.

What About Including the Odds?

This is a hotly debated topic in the sports betting community. Bill Benter, one of the fathers of algo betting, argued that the odds are best to be included because they encode so much information. Having been testing this hypothesis for many thousands of hours, my conclusion is that if you don't have a certain level of extremely high quality engineered features, then yes you should include the odds. But at a certain point, the features you engineers will actually encode more information in combination than the odds do. At that point, including the odds simply lowers the ROI.

Mathematical Mechanism

When you include odds as a feature, you're introducing a variable that represents the market's aggregated probability estimate: P_market(fighter1_wins). This creates several mathematical problems:

1. Feature Dominance and Prediction Convergence
Tree-based models will heavily weight the odds feature because it exhibits high mutual information with the target across the entire dataset. The model's predicted probabilities become:

P_model(fighter1_wins) ≈ α·P_market + (1-α)·P_stats where α > 0.5

This forces convergence toward market consensus.

2. Outcome Distribution Skew
Including odds biases the model toward predicting high-frequency, low-profit outcomes (favorites). Your engineered statistics without odds bias toward identifying low-frequency, high-profit outcomes (underdog value).

3. +EV Prediction Accuracy Inversion
The critical insight: ROI optimization requires accuracy specifically on profitable bets, not overall accuracy.

• With odds included: Model achieves ~74% accuracy but concentrates correct predictions on favorites (odds = 1.2-1.8, profit margin = 20-80%)
• Without odds included: Model achieves ~71% accuracy but concentrates correct predictions on underdogs (odds = 2.5-4.0, profit margin = 150-300%)

ROI Mathematics

Consider two hypothetical models:

• Model A: 75% accuracy, predicts favorites 85% of the time → Expected ROI ≈ -2% (high accuracy, low margins, vig erosion)
• Model B: 50% accuracy, predicts underdogs 60% of the time → Expected ROI ≈ +15% (lower accuracy, exponentially higher margins)

The fundamental equation:

ROI = Σ(accuracy_i × frequency_i × profit_margin_i)

Your empirical results demonstrate that excluding odds increases accuracy_underdog dramatically while slightly decreasing accuracy_overall. Since profit_margin_underdog >> profit_margin_favorite, the ROI optimization occurs through maximizing performance on the subset of predictions with the highest profit potential.

Information Compression Loss

Odds represent market consensus based on public information flow. Your engineered features capture orthogonal signals that specifically identify cases where statistical analysis diverges from public perception—exactly the scenarios that generate +EV opportunities. Including odds suppresses these divergent signals in favor of consensus alignment, destroying the edge that creates profitable betting opportunities.

The Vanity Metrics Problem in Machine Learning

You will see many other novice machine learning engineers practice their skills against sports prediction. They will calibrate their models against vanity metrics like accuracy in most cases. They will see evaluations like 85% accuracy, then not have any motivation to figure out why their model will fail in the real world then make a YouTube or Medium post about it.

This represents the fundamental disconnect between academic machine learning and profitable real-world application. The sports prediction space is littered with impressive-sounding accuracy claims that evaporate when subjected to actual betting markets. These engineers optimize for metrics that sound impressive in blog posts rather than metrics that generate alpha.

The vanity metrics obsession creates a particularly insidious blind spot: data leakage and overfitting become invisible when you're chasing high accuracy numbers. Consider the classic example in YouTube tutorials (https://www.youtube.com/watch?v=LkJpNLIaeVk) where a model achieved impressive accuracy predicting UFC fights using Elo ratings... except they used post-fight Elo ratings for training, meaning the model literally saw fight outcomes during training. This is textbook data leakage: using future information to predict past events.

Data Leakage Examples in Sports Prediction:

• Training on post-game statistics to predict game outcomes
• Including betting line movements that occurred after the event
• Using season-end rankings to predict mid-season games
• Including opponent-adjusted metrics calculated after the fight

The overfitting trap compounds this problem. Hyperparameters are the configuration settings that control how a model learns: things like learning rate, tree depth, regularization strength. I can easily tune these hyperparameters to achieve 78% accuracy on my validation set by optimizing for that specific data slice. But this creates a model that memorizes the validation set's quirks rather than learning generalizable patterns.

The feedback loop is broken: High accuracy on test data → immediate gratification → publish results → never discover real-world failure. There's no motivation to dig deeper because the vanity metric has been satisfied. The engineer never learns that their 85% accuracy model would lose money consistently because they never actually test it against betting markets.

Real-World Adversarial Markets

Real-world sports betting is an adversarial market where you're competing against:

• Professional odds compilers with decades of experience
• Sophisticated betting syndicates with proprietary data
• Market makers who adjust lines in real-time based on money flow
• The inherent vig that makes break-even betting a losing proposition

Simply achieving high accuracy on historical data means nothing if your predictions can't consistently identify mispriced markets. The difference between academic exercise and profitable application is the difference between predicting outcomes and finding edges.

Lessons from Four Years of Iteration

I'm four years into this space and I've made all the same mistakes. I've built models that achieved 78% accuracy and lost money consistently. I've spent months optimizing for log loss improvements that translated to worse ROI. I've fallen into every trap outlined above because the feedback loop between model performance and real-world profitability is opaque until you actually start tracking betting results over extended periods.

This is a far more complex problem than I ever initially thought 4 years ago, but I believe what's outlined above is one of the reasons I've been seeing almost 20% ROI over the past few years in my free, public predictions. The key insights around dataset balancing, odds inclusion, and ROI-focused optimization came from years of iterative failure and debugging, not from following standard ML tutorials.

The engineering rigor required to build profitable models demands treating accuracy as a vanity metric and ROI as the only metric that matters with the knowledge that betting markets shift as time goes on and you must constantly retrain the model to match the current zeitgeist. Hence why I'm on version 6.3 right now. I've redone 100% of the code 6 times now. If you want to avoid the same mistakes I've made, feel free to reach out. I'm an open book on exactly how I built this model, no secrets. And also, as usual, shoutout to Chris from Wolftickets.ai for being one of the very very few people in this ML for sports prediction field that actually shared his technical knowledge and saved me endless hours of wasting my time. I like paying that forward to others who are interested in this space.

I have released v6.1 of the model. Large improvement in accuracy but most specifically in ROI. So let's talk betting strategy. One question I get asked practically every day is, "why do you recommend only the AI picked winners even if they're not +EV?"

The best tech available for predicting UFC are binary classification algorithms. These are algorithms specialized in classifying a fighter as either 1 or 0, win or loss. The confidence score that the algorithm comes up with is not its fundamental strength.

"So why don't you calibrate it?"

Because the calibration tech we have for these algorithms suck. Platt Scaling and Isotonic Regression are the two most potent weapons we have to calibrate these predictions. I have experimented a lot with them. 100% of the time they suck. They lower the accuracy and the ROI. I've experimented with custom calibrations but it's just too inconsistent and I don't see a promising way forward. I would absolutely love to have better calibration, so if you have any ideas please let me know. That being said, the ultimate goal here is risk-adjusted returns. Calibration is a tool to help us get there but it's not necessary to acheiving the goal.

Anyway, who cares about calibration if we're making fat ROI? Take off your sports bettor hat and all the "fundamentals" you know like +EV is all that matters to be successful. Put on your machine learning cap and look at the data. This is the calibration curve:

Note how the model is highly underconfident in its 50-65% confidence score picks and highly overconfident in it's 35-50% confidence scores. The nature of the algorithm is to maximize it's ability to successfully pick the winner and it does this at the expense of accurate calibration. It clusters it's confidence scores in the 50-65% range. AND THAT'S OK!

Here's the model evaluations and vegas evaluations on the last year of unseen fights:

Note the model is more accurate than Vegas, but it's logloss and Brier scores (essentially real world win%) are worse. Again, THIS IS OK. Why? Because look at these profit strategy backtests over the last year of unseen fights:

The fundamental strategy of betting on 100% of the AI picks on the closing odds is 14% profitable (ai_all_picks_closing). The strategy of picking only the +EV fighter based on the AI confidence score whether the AI picked that fighter to win or not is -0.5% unprofitable (any_fighter_positive_ev_closing).

Interpreting The Strategies

None of this is to say that +EV isn't a helpful metric. Look at another fundamental strategy, betting only on +EV AI-picked fighters (ai_picked_positive_ev_closing): +24.2% ROI. 10% higher than just doing down the line bets but it means sometimes there'll be events where you don't get to bet which makes me sad.

So let's put this all together. Why are parlays so good with this machine learning algorithm? It's because the algorithm is so gosh darn good at picking winners. Parlaying the AI picks, whether +EV or not, is a highly profitable strategy. The best strategy is doing 2 to 3 leg parlays on the +EV AI picked fighters. I'll probably move into posting these parlays again in the homepage.

---

EDIT: Shoutout to @Heisenb3rg on X for bringing Sharpe Ratios to my attention! This is a crucial metric from finance that measures risk-adjusted returns. Essentially, it tells us how much return we're getting for the amount of risk (volatility) we're taking on with a particular betting strategy. A higher Sharpe Ratio is better.

Looking at the Sharpe Ratio analysis, we can see how different strategies compare not just on raw ROI, but also on how bumpy the ride is. For v6.1, the 'ai_picked_positive_ev_closing' strategy seems to offer a strong balance, providing good returns without excessive risk compared to some others. However, the 'ai_all_picks_closing' still performs well from a risk-adjusted perspective, offering broader betting opportunities.

So, what's the takeaway? While different model versions might favor underdogs or favorites differently, the data consistently points towards a simple, robust approach. Considering both the ROI and the Sharpe Ratio (risk-adjusted return), the strategy of betting on all AI picks using the odds available 7 days before the event (ai_all_picks_7day) emerges as the winner. It offers the best blend of profitability and lower volatility, making it the simplest and most effective core strategy based on the current analysis.

It's important to remember that model performance, especially regarding favorites versus underdogs, can shift between versions and timelines. Therefore, relying solely on specific odds ranges like underdogs only might be less reliable long-term despite being very profitable over the past year. Instead, I think focusing on fundamental strategies evaluated through metrics like ROI and Sharpe Ratio is key. For the current model, based on the patterns I've seen over the years, I think I'm going to stick with the core strategy ai_all_picks_sevenday which provides the best risk-adjusted performance indicated by the Sharpe Ratio. To get higher returns at higher risk, 2 to 3 leg parlays of your choice are a good option.

Here are the AI predictions for UFC 314.

Check out the latest video analysis and AI predictions for the upcoming UFC matchup between Emmett and Murphy. The AI generated interpretation of my face always cracks me up.

Check out our latest video explaining how MMA-AI makes its predictions and why our model has been consistently outperforming Vegas odds.

After countless requests from the community, I'm finally pulling back the curtain on how our UFC fight prediction algorithm works. This isn't just another black-box system—it's a carefully engineered, multi-level approach to fight analysis that's consistently outperforming Vegas odds.

Why Share Our Secret Sauce?

Many have asked why I'd reveal the inner workings of a profitable system. The truth is simple: I don't believe in keeping this knowledge secret. Much of this algorithm was developed with the assistance of AI tools that generated about 90% of my code. As someone who's been an open source developer for 15 years, I firmly believe that open knowledge sharing accelerates human progress. I don't have a moat to protect—and frankly, the more people who understand these concepts, the faster our collective knowledge will advance. Sports prediction is hard enough that even with this blueprint, you'll still need to invest thousands of hours to truly master it.

The Four Levels of Fight Prediction

Level 1: Foundation Stats + Bayesian Gamma-Poisson Smoothing

We start with raw fight statistics—strikes thrown, takedowns landed, control time, and dozens more. But raw numbers can be misleading, especially for rare events like submissions. This is where Bayesian Gamma-Poisson smoothing comes in.

Imagine a fighter who's attempted only one submission in their career and landed it. Is their submission accuracy really 100%? Probably not. Gamma-Poisson smoothing helps us balance observed data with prior knowledge, preventing outliers from skewing predictions. For high-volume stats like significant strikes, the smoothing effect is minimal. But for rare events like submissions or knockdowns, it provides crucial stability by "pulling" extreme values toward more realistic expectations based on the fighter's division and overall UFC averages.

Level 2: Comparative Analysis

Next, we calculate a fighter's efficiency metrics: accuracy (how often attacks land), defense (how often they avoid opponents' attacks), output per minute, and the ratios between fighters across all statistics. This gives us a clearer picture of how fighters perform relative to each other, beyond just counting actions. A fighter might land fewer strikes overall but have significantly higher accuracy—a crucial distinction our model captures.

Level 3: Time-Weighted Averages + Variability

MMA evolves rapidly, and a fighter today isn't the same as they were three years ago. We calculate both standard and time-decayed averages with a 1.5-year half-life for all statistics. This means a fight from three months ago has far more impact on our predictions than one from three years ago.

Additionally, we measure the variability of these stats using Median Absolute Deviation (MAD) instead of standard deviation. MAD is less affected by extreme outliers, providing a more stable measure of how consistent a fighter's performance has been.

Level 4: Adjusted Performance (AdjPerf)

Our most sophisticated metric answers a critical question: how does a fighter perform against a specific opponent compared to how that opponent's previous adversaries performed? This z-score normalization looks like:

stat_adjperf = (fighter1_stat - fighter2_stat_prev_opp_avg) / fighter2_stat_prev_opp_mad

In plain English: we're measuring how much better or worse a fighter performed against their opponent compared to what we'd expect based on the opponent's history. If a fighter lands more strikes against someone who's historically difficult to hit, that's far more impressive than landing the same number against someone who's easily hit. AdjPerf captures this crucial context.

Building the Prediction Model

With thousands of engineered features from these four levels, we use Autogluon (thanks to Chris from Wolftickets.ai for this recommendation) to train our prediction model. Using presets like "experimental" and time-ordered data splitting (typically 80/20 or 90/10 train/test), we run extensive cross-validation to ensure reliability.

There's no definitive guide to sports prediction—we've conducted thousands of hours of testing to find what consistently beats Vegas odds. Everything from feature selection to hyperparameter tuning requires constant experimentation and refinement. What works for NFL might not work for UFC, and what worked last year might not work next year.

The final model combines about the 30 best of these features, weighted according to their predictive power. The result is a system that consistently identifies value bets where our predicted win probability exceeds what Vegas odds imply.

The Practical Limitations of ML Probabilities

One of the humbling lessons I've learned over the years is about the relationship between machine learning and betting strategy. Despite the sophisticated nature of our model, I've had to accept that ML algorithms have inherent limitations when it comes to probability calibration. While traditional betting approaches rely heavily on expected value (EV) calculations, I've discovered that applying these same principles directly to ML outputs can be problematic. Our tabular ML models excel at binary classification—essentially determining which fighter is more likely to win—but their confidence scores aren't necessarily true probabilities in the statistical sense. Even when optimizing for log loss (which theoretically improves probability calibration), there remain subtle biases and distortions in how these models estimate probabilities. Through trial and error, I've found that treating the model's outputs as relative confidence levels rather than exact win probabilities leads to more consistent results. Instead of rigidly applying EV formulas, we use confidence thresholds as a filtering mechanism to identify promising bets. This pragmatic approach acknowledges the model's strengths in pattern recognition while respecting its limitations in precise probability estimation—a balance that has proven more effective than assuming perfect calibration.

Why Current LLM-Based Fight Predictions Fall Short

I've extensively tested Large Language Models (LLMs) like GPT-4 for fight predictions, and the results have been consistently disappointing. The fundamental limitation is clear: today's LLMs lack the ability to analyze fight footage. They're trained primarily on text data, which means they miss crucial visual information—a fighter's movement patterns, subtle defensive vulnerabilities, changes in stance, or signs of fatigue that only appear on video. Statistical data can tell us a lot, but the visual dimension of fighting contains irreplaceable insights that no spreadsheet can capture. The good news? This limitation is temporary. Within the next 1-2 years, we'll see multimodal AI systems trained on vast libraries of video footage, capable of analyzing thousands of fights frame-by-frame. When that happens, AI fight prediction will undergo a revolutionary leap forward. Until then, the most effective approach remains combining sophisticated statistical modeling with human expertise for context and interpretation.

Conclusion: The Never-Ending Journey

MMA prediction remains as much art as science. While our technical approach provides an edge, the sport constantly evolves, and so must our model. Every event brings new data, every fighter brings new patterns, and our system continually adapts to these changes.

Whether you're a casual fan or a serious bettor, I hope this behind-the-scenes look helps you appreciate the depth of analysis that goes into each prediction you see on MMA-AI.net. And if you're inspired to build your own model? Even better—innovation thrives when knowledge is shared.

Model v6 is available for tonight's event and events going forward. This is intended to be a long-term release.

Changes:

• Unit tests for everything
  • Finally we have unit tests for all calculations so I can sleep at night. At least now if the model fails I know it's not some unknown bug.
• Bayesian Gamma-Poisson
  • We switched out from just doing Bayesian Beta Binomial smoothing in accuracy/def and per_min calculations to a Bayesian Gamma-Poisson for all stats starting at the very beginning. This is a more robust and consistent smoothing factor.
• Swapped stddev for median absolute deviation for the zscore normalization stat adjperf
  • Adjperf layer of feature engineering changed from:
    stat_adjperf = (fighter1_stat - fighter2_stat_prev_opponents_avg) / fighter2_stat_prev_opponents_stddev
    to:
    stat_adjperf = (fighter1_stat - fighter2_stat_prev_opponents_avg) / fighter2_stat_prev_opponents_mad
  • Median absolute deviation (MAD) is a more robust measure of deviation for sports statistics because it's not as vulnerable to outliers.

Future:

Have a few stats I'd still like to engineer especially around the win conditions of submissions vs KO vs decision.

I have also added visualizations to the predictions. Just hover over the fight or click on the fight to see how each fighter compares to each other using a normalized stat difference. Note that these visualizations do not account for how the model is weighing each stats, it's just the normalized difference in the stats between the fighters to give you an idea of where each fighter has an advantage. Larger surface area = better stats but you may notice sometimes the fighter with the larger surface area is not picked, this is due to the fact the stats are not weighed equally by the model and also because the model makes some complex relationships between the stats that won't be reflected by the visualization.

Based on the past 2 months of performance I'm fairly convinced I have some bugs in the nonunit tested code. I've started the unit testing but I'm not done yet so take this event (3-1-2025 UFC Fight Night) with a grain of salt, might be a good one to skip for now, but I should have lots of time after work to finish unit testing next week and I'll post an update about bugs found once I'm done.

After countless hours of trial and error testing this week, we're implementing a few key refinements to the model. Rather than making sweeping changes, we're focusing on targeted improvements that have shown consistent benefits in our testing:

1. Updated Training Data Window

We're moving the cutoff date for training data from 2014 to 2016. While I've been using 2014 as the starting point for the past 4 years, it's time to shift forward to better capture recent trends in the sport. MMA evolves rapidly, and data from 10 years ago may not be as relevant to today's fighting landscape as it once was.

2. New Feature: UFC Age

We've added a simple but effective new stat: UFCAge. This measures the amount of time a fighter has been in the UFC. While straightforward, this metric helps capture valuable information about a fighter's experience at the highest level of competition.

3. Enhanced Feature Layering

Previously, we were using two primary layers of features:

• Decayed adjusted performance (dec_adjperf_dec_avg)
• Opponents' decayed average (opp_dec_avg)

Now we're adding a third layer: the fighter's individual stats (like strikes_landed_ratio_dec_avg). This addition has proven valuable - by combining all three layers of a key base stat (like head_landed_ratio), the algorithm seems better equipped to predict how each fighter will perform relative to the broader UFC population.

Looking Forward

I'm preparing to start producing analysis videos to help explain the model's decision-making process and break down specific fight predictions. The site has been updated with the latest calibration curve, model evaluations, and feature importance rankings to reflect these changes.

As always, these updates are focused on one goal: improving our ability to predict fight outcomes accurately. The changes might seem subtle, but in the world of fight prediction, small edges often make the difference.

Goddamn that took forever. There was a bug in the zscore normalization stat I named _adjperf. If you recall, the calculation for adjperf is:

stat_adjperf = (fighter1_stat - fighter2_prev_fight_stat_opp_avg) / fighter2_prev_fight_stat_opp_sdev

• f2_stat_opp_avg is the historical opponent average against fighter2 pulled from fighter2's previous fight.
• f2_stat_opp_sdev is the historical opponent standard deviation pulled from fighter2's previous fight.

This stat is extremely complicated to implement and was the reason we were predicting so few fights ever since v5 was released with it included. We train with only data known pre-fight so we shift all the data backwards by 1 fight for all fighters. The consequences:

Case #1:

All fights where at least one fighter is debuting are immediately eliminated because their data is 100% null after we shift the data backwards by 1 fight and we can make no comparisons between them and their opponent.

Case #2:

All fights where at least one fighter has only 1 previous fight is useless because one-previous-fight fighter has a 0 in fighter2_prev_fight_stat_opp_sdev for their opponent's adjperf calculation.

Case #3

One fighter has 3 previous fights, the other fighter has 2. Again, adjusted_performance for fighter1 will be 0.

And so on. It means that _adjperf is causing an enormous amount of fights to be dropped.

I've tried to fix this by calculating an initial standard deviation for all first time fighters. I collect all stats of first-time fighters on a per weightclass, per stat basis. So your _adjperf score against first-time fighters is based on how good or bad you did compared to the median first time fighter's stats. This feels fine, because we're dropping all fights where either fighter only has 2 previous fights anyway.

Bug Fixes

So there was a fun little bug affecting ~2% of the training data where fighter2_stat_opp_sdev would end up being 0.00000002 or something so the adjperf score would end up being like 11,839,902 instead of a more normal 1.5 or -1 (i.e., fighter1 scored 1.5 standard deviations above what fighter2 usually allows in that stat from their historical opponents). The reason was because I only use time-decayed averages in the final model to capture recent trends in both fighters and their opponents and the time-decayed standard deviation calculation is a bit complex:

weight = EXP(-λ * ((T - t) / 365.25))

Sooooooometimes, T = 7.777777777 and t = 77.77777778 due to rounding in Postgres double precision. I have fixed this by capping the minimum standard deviation of stats to their 5th percentile. This is to avoid insane standard deviations in tiny edge cases like Khamzat Chimaev's early UFC run where his opponents only scored like 4 strikes against him in 4 fights then he fought Gilbert Burns who hit him 223 times. This meant Burns' _adjperf score was insane because he took Khamzat like 400 standard deviations away from his previous opponent averages.

Last, I had some small bugs affecting the filtering of training data. The order of filtering the data matters a LOT and I was doing some dumb stuff like filtering out Draws and stuff, THEN calculating number of fights for each fighter and filtering on number of fights which is wrong because I already filtered out fights before calculating number of fights for each fighter.

OK! That about wraps up the updates this week. It took a really long time to get through all those bugs so I'm trying to get the updated predictions out before this event, bear with me.

First, we're changing the wording from "AI win%" to "AI confidence". This is to sort out the confusion that many traditional bettors have. This algo is not specialized in finding +EV. It is a binary classification algorithm, meaning it is very good at figuring out who will win, but not the real world win % chance. Predictor.predict(upcoming_fights) returns a binary value of 1 = fighter1 predicted to win, 0 = fighter1 predicted to lose. We can do predictor.predict_proba(upcoming_fights) and get it's best guess at each fighter's implied probability but generally this probability is not well-calibrated because this is specifically a binary classifier.

Second, the reason we're doing parlays is because they're essentially a multiplier of the profit from the single picks. You can risk less units to win more. You don't have to do this, you can just do the straight picks and limit the boom and bust cycle of the parlay strategy, but backtesting is showing the parlay strategy consistently outperforms the straight picks in ROI.

On this note, up until now I've been randomly creating the parlays. I've been trying to figure out how to get rid of that randomization. Sorting the fights by AI confidence or inconfidence ended up performing worse than random picks. So I thought about what does the algorithm crave to become more accurate? Data.

The new parlay strategy is based on backtesting showing more consistent results by sorting the parlays by total combined fights both fighters have had. Islam has had 15 fights in the UFC. Renato Moicano has had 17 fights. That's 32 fights of data that the algorithm has had time to calibrate on. So whatever the algorithm picks on this fight is likely to have the most consistent accuracy. That's why we're seeing islam in 3 parlays this event.

This strategy could use more refinement, and ideally we'd actually just create every possible 3 leg parlay and set that up as the predictions for every event. The only reason I don't do that is because it takes forever to input all those parlays into betmma.tips and the bookie but maybe once I automate the placing of pre-event picks into betmma.tips or something then I'll start doing all parlay combinations possible as the recommended picks.

Alright, so I'm finally ready to talk about my new key feature: Adjusted Performance. This has been one of those "why didn't I think of this sooner" moments, but also "holy crap this is a nightmare to implement." Let me give you a quick taste of what it looks like mathematically:

fighter1_stat_adjperf = (fighter1_stat − fighter2_stat_opp_avg) / fighter2_stat_opp_sdev

We'll call this f1_stat_adjperf for short. The big idea is to measure how much a fighter's performance in any given fight exceeded or fell short of what we'd expect their opponent to allow. If you go in there against some unstoppable jab machine who normally forces everyone to eat 50 jabs per round, but you manage to hold them to only 20, well, that's huge. But if you never do the math to figure out what your opponent's "baseline" is, you'll just record "Fighter1 absorbed 20 jabs" and maybe think it's not that great. Meanwhile, that's incredibly good compared to the 50 jabs everyone else took. Hence, adjusted performance.

Understanding the _opp Suffix

Before going any further, let's talk about the _opp suffix. First, _opp is the post-fight stats your opponent did against you. So if you see something like f2_stat_opp_avg, that means the stat is referencing "what your opponent's opponents did against them." For example:

• f1_stat_opp_avg: The average of your opponents' performances against you in all their fights.
• f2_stat_opp_avg: The average of your opponent's opponents' performances against your opponent in all their previous fights.
• f2_stat_opp_sdev: The standard deviation of your opponent's opponents performance in those same fights, giving us a measure of the volatility or variability in their performance.

So, if your opponent has 40 strikes landed against them then f2_strikes_opp_avg is 40.

This means, to measure your adjusted performance, you compare your post-fight stat in the fight to their pre-fight _opp_avg, and then scale it by pre-fight _opp_sdev. If you get 60 strikes against someone who averages getting hit 30 times, you're 1 standard deviation above average against that person.

Why It's So Valuable

Let's be honest: raw stats can lie, or at least mislead. If a fighter's output is just "I landed 30 strikes," that doesn't tell me how many strikes they should have been able to land. If they were fighting an iron-clad defensive wizard who typically only allows 10 strikes, then landing 30 is insane. On the flip side, if your opponent is basically an open punching bag who gives up 60 strikes on average, then landing 30 is actually pretty weak.

Adjusted performance changes the game: it says, "30 strikes might be good or bad, but let's see how it compares to what your opponent usually allows." Then, for even more nuance, it's scaled by the opponent's historical standard deviation—so you don't artificially inflate your stats just because you faced someone with wide variability on a certain stat.

The Complexity: Where Do You Even Get These Numbers?

The problem with pulling off something like f1_stat_adjperf is that you actually have to calculate your opponent's _opp_avg and _opp_sdev. In other words:

• Grab all your opponent's previous fights.
• For each of those fights, figure out the stats they allowed to their opponents.
• From that, compute the average allowed stats and the standard deviation of those stats.
• Then bring that back into your current fight to see how well or poorly you did.

This is where the data pipeline can get insane, because you might have a fighter who has 15 or 20 fights, each with a different set of opponents. Some of those opponents have 30 fights apiece. Doing this for every fighter means you need to traverse a huge web of fight stats.

If you run a naive approach—like just using Panda's groupby and merges all day—it becomes unbelievably slow at scale. This is why I had to do some major refactoring, rewriting a chunk of my data pipeline to pull from a properly indexed database (Postgres, in my case). Once your data is properly structured, it's much faster to do these calculations in a single pass or via specialized queries, rather than stumbling around in memory merges.

Time-Decayed Averages & Time-Decayed StdDev

But wait—there's more. I decided to do a time-decayed average (and corresponding standard deviation) with a 1.5-year half-life. That means that a fight 3 months ago is given a lot more weight than a fight 5 years ago, which is basically ancient history in fight years.

Now the complexity is multiplied by, like, a factor of 10. Because to get f2_stat_opp_avg, I can't just average everything your opponent has done; I have to:

• Grab each fight's stat.
• Weight it exponentially based on how recently it happened.
• Sum up those weighted stats.
• Divide by the sum of the weights.
• Then do it all over again for the standard deviation.

And let's not forget: we do this for every single fight, across thousands of fights, across hundreds of fighters. That's why I always say data engineering is half the battle.

Why Bother?

So why go through this code-wrangling fiasco when your standard raw stats might be "good enough?" Because fights are context-dependent. If you have a stand-up specialist with insane takedown defense, but no one has tested it in years, your raw stats might not reflect the real picture of how they handle a brand-new style. By blending in adjusted performance stats, you're no longer stuck just describing how many strikes or takedowns a fighter landed; you're describing how well they did compared to what their opponent typically experiences—and you're discounting or boosting older fights according to their recency.

This is how we start to see nuanced differences that no raw stat alone can show. It's the difference between "Fighter A landed 40 strikes" vs. "Fighter A forced a 1.5 standard-deviation drop in Fighter B's typical striking output." That second statement captures so much more power. If you can integrate these insights into your model, you get a far more realistic prediction of how a matchup might turn out.

v5 beta is *might* be done in time for the next event. I'm 100's of hours in. The data processing and model training is basically done, I just need to figure out the final feature set and do some tuning. Then I need to write the future prediction code for creating and cleaning the data of future fights. Finally, we're beating Vegas accuracy/log loss without including the odds or rating/ranking stats like an Elo score. That's not to say I won't include those in the future, but it's a great sign that the fundamentals of the model are improving. I would like to thank my $200/mo ChatGPT o1 Pro subscription for making this possible. That model absolutely rules at complex code, especially statistics and math.

Here's a recent training run to give you an idea of current levels of performance. This isn't the final model performance, it's just from tinkering with the feature set and training parameters:

Model Performance:
Training log loss: -0.611
Validation log loss: -0.575
Test Log loss: -0.612
Training accuracy: 0.671
Validation accuracy: 0.698
```