Kelly Criterion Calculator

The Kelly criterion is a sports betting bankroll formula that tells you what fraction of your bankroll to risk on a bet to maximize long-term growth. The formula is f* = (bp − q) / b where b is the net odds (decimal odds minus 1), p is your estimated true probability of winning, and q is the probability of losing. The result is the fraction of bankroll that — bet repeatedly under the same conditions — produces the highest geometric growth rate.

In practice, full Kelly is too volatile for most bettors. A losing streak can easily wipe 40-60% off your bankroll even when your edge estimate is correct, because the formula assumes your true probability is known with certainty. Most professionals use half Kelly or quarter Kelly — same long-term ranking of edges, dramatically smaller drawdowns. This calculator defaults to half Kelly for that reason.

The expected growth rate shown above isn't your average return on stake — it's the per-bet expected log-growth of your bankroll, which is what Kelly actually maximizes. A 0.3% growth rate compounds to about 26% over 100 bets if your edge holds. The 100-bet trajectory chart shows three illustrative paths (10th percentile, median, 90th percentile) so you can see what variance looks like at the stake size you've chosen — a small number, repeated.