Kelly Calculator
Kelly Criterion calculator for sports bettors.
Optimal stake sizing for long-term growth. Enter your edge, odds, and bankroll — get full, half, and quarter Kelly recommendations.
The Kelly formula
f* = (bp − q) / b, where b = decimal odds − 1, p = your estimated win probability, q = 1 − p. The result is the fraction of your bankroll to wager.
Example: +150 odds (b=1.5), your model gives 45% (p=0.45, q=0.55). f* = (1.5 × 0.45 − 0.55) / 1.5 = 0.083 — bet 8.3% of bankroll at full Kelly.
Why fractional Kelly
Full Kelly is the mathematically optimal growth rate, but variance is brutal — 33% drawdowns are routine. Half Kelly cuts variance by 75% while keeping most of the growth. Most pros stake at quarter or half Kelly.
Kelly for +EV scanners
Parlae's EV scanner attaches a Kelly-recommended stake to every +EV play, scaled to your bankroll and risk tolerance setting (full / half / quarter).
Frequently asked questions
What is the Kelly Criterion?
Kelly is a bankroll-management formula that calculates the bet size maximizing long-term geometric growth given a known edge. f* = (bp − q) / b where b is decimal odds minus 1, p is win probability, q is loss probability.
Should I use full Kelly?
Most pros use quarter or half Kelly because full Kelly assumes perfect edge estimation. If you overestimate edge by even 10%, full Kelly leads to massive drawdowns. Half-Kelly halves variance while keeping ~75% of growth.
Does Kelly work for parlays?
Yes, but you need a calibrated probability for the parlay as a whole — not the product of leg probabilities. Parlae's parlay calculator returns Kelly-sized stakes automatically.
Can Kelly stake be negative?
If the formula returns negative, the bet is -EV and you should not place it. Parlae shows '$0' rather than a negative number.