Calculate expected value, ROI, Kelly stake, accumulator returns and implied probability for any football bet. All tools are free, no account required.
Every calculator on this page is free to use. See how our model probabilities are calculated.
Profitable sports betting is not about picking winners. It is about understanding probability, expected value, and bankroll management. The calculators on this page give you the tools to approach every bet as a mathematical decision rather than an emotional one. They work alongside xGaura's value bet index and Poisson model predictions to help you size stakes correctly, identify true edge, and project long-term results.
Expected value (EV) is the single most important concept in sports betting. It answers the question: on average, how much will I win or lose per unit staked on this bet? The formula is simple: EV = (probability of winning × profit if won) − (probability of losing × stake). A positive EV bet is one where the mathematical expectation is profitable. Over a large sample of positive EV bets, you will profit regardless of short-term variance. Enter your model probability from xGaura's mathematical predictions and the bookmaker's decimal odds to calculate EV instantly.
The Kelly Criterion is a mathematical formula for calculating the optimal stake size on any bet with a positive edge. Full Kelly stake = (edge / odds − 1). In practice, most professional bettors use a fractional Kelly — typically 25% or 50% of the full Kelly amount — to reduce variance while preserving the mathematical advantage. The calculator above defaults to 25% Kelly (0.25 fraction), which is the most commonly recommended setting. Using Kelly ensures your stakes scale with the size of your edge and your bankroll, preventing overbetting on low-edge selections.
Bookmaker odds always include a margin — the overround — that guarantees the bookmaker a profit regardless of the outcome. To find the true implied probability of any selection, you need to strip this margin out. The implied probability calculator above accepts decimal, fractional and American odds, and allows you to enter the bookmaker's estimated margin to derive the fair probability after margin removal. Comparing this fair probability to your model probability reveals the true edge on any bet.
Accumulators multiply individual odds together to produce a combined price. The accumulator calculator on this page also calculates the combined win probability across all legs — which is the product of each leg's individual probability. This is the number most recreational bettors never calculate before placing an acca. A four-fold accumulator with each leg at 65% win probability has a combined probability of 0.65 × 0.65 × 0.65 × 0.65 = 17.9%. If the combined odds imply a probability higher than that, the acca has positive expected value. If not, it does not.
The bankroll growth simulator projects your final bankroll over a given number of bets, assuming a fixed percentage stake, consistent average odds and a given win rate. It uses the geometric mean return to model compounding growth, which is more realistic than a simple linear projection. Use it to understand what a 2% stake per bet at 62% win rate on 1.85 odds actually looks like over 100 or 200 bets — and to stress-test your staking strategy before committing real money.
All calculators on this page are for informational and educational purposes. No prediction is guaranteed. Bet responsibly. You must be 18 or over to gamble.