Kelly Criterion Calculator

Kelly Criterion Bankroll Calculator

The Kelly Criterion tells you the mathematically optimal fraction of your bankroll to bet on a positive-EV opportunity to maximise long-run growth without risk of ruin. Used by professional sports bettors, poker pros, and quant funds. Casino slot bets are negative-EV — Kelly says bet zero. Use this for sportsbook, poker, or arbitrage situations where you genuinely have an edge.

The formula

f* = (b × p − q) / b, where:

• b = decimal odds − 1 (net profit per unit wagered)
• p = your assessed win probability
• q = 1 − p (loss probability)
• f* = optimal fraction of bankroll to wager

If f* ≤ 0, you have no edge — bet zero. If f* is positive, full Kelly maximises long-run geometric growth. Most professionals use half-Kelly or quarter-Kelly because real-world probability estimates are noisy: betting full Kelly with overconfident probabilities risks ruin.

When to use Kelly

• Sportsbook bets where you have a documented edge over the closing line (e.g. soft books, market inefficiencies, niche leagues you know well).
• Poker: implied odds calculations, stake selection, bankroll allocation.
• Arbitrage / matched betting: sizing the larger leg of an arb.
• NOT for slots, crash, mines, dice, plinko — all are negative-EV. Kelly says bet zero. Anyone telling you otherwise is selling something.

Practical caveats

Kelly assumes you know your true win probability. In sports betting, your edge is usually 1–5% — turning that into Kelly fractions means tiny bet sizes (1–5% of bankroll). If your "edge" is based on gut feel, your real probability is closer to the implied odds — Kelly says bet ~zero. The hardest part of Kelly is honest self-assessment.

← All tools · How we test