This free calculator does the three sums that matter when betting with discipline: implied probability, expected value (EV) and the optimal stake by the Kelly criterion. Enter your numbers and try it.
Value bet & EV calculator
What is a value bet?
A value bet is a bet whose true probability is higher than the one the odds reflect. Odds hide an implied probability (1 ÷ odds); if you estimate the event is more likely than that, you have value. Systematically betting positive value is what makes a bettor profitable long-term, even while losing individual bets.
The expected value (EV) formula
Expected value measures how much you win or lose on average per unit staked: EV = (probability × odds) − 1. If positive, the bet has value; if negative, the market is overcharging you. For example, with 55% probability and odds 2.00: EV = 0.55 × 2.00 − 1 = +0.10, i.e. +10% per unit.
The Kelly criterion: how much to stake
The Kelly criterion computes the optimal percentage of your bankroll to stake to maximize long-term growth: f = ((odds−1) × p − q) ÷ (odds−1), where p is your probability and q = 1−p. In practice, use quarter Kelly to reduce variance. The calculator shows both.
Frequently asked questions
Is the calculator free?
Yes, it’s 100% free and requires no sign-up. It’s designed so any bettor can tell whether a bet has value.
Where do I get my estimated probability?
From your own analysis or a model. gambeta.ai’s AI predictions already give you a probability and an odds to compare.
Why quarter Kelly and not full Kelly?
Full Kelly maximizes growth but with high variance. Fractional (¼) grows almost as much with far less risk of harsh runs.
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