Bankroll

Kelly Criterion Calculator

Odds, win probability, bankroll in. Optimal stake out. Quarter Kelly by default; $0 when the bet is −EV.

Inputs

Odds

Implied probability: 52.4%

Win probability (%)

Your true estimate of how often this bet wins.

Bankroll ($)

Total betting bankroll, not your monthly budget. Kelly assumes you can re-bet.

Kelly fraction: 0.25×

Quarter Kelly (0.25×) is the conservative default. Full Kelly maximizes growth but ruins you on a single bad input.

Try a preset

Recommended stake

$13.75

1.38% of bankroll

Full Kelly would be $55.00 (5.50%).

Edge

+2.62pp

Implied 52.4%

Expected value

+$0.69

5.00% per $ wagered

True win prob

55.0%

Your estimate

Growth rate

0.060%

Log-growth per bet

Kelly assumes (a) your probability estimate is correct and (b) you'll keep re-betting from the same bankroll. Real bettors should size below full Kelly to absorb estimation error. Quarter Kelly is the convention.

How Kelly works

The Kelly criterion answers one question: given an edge, what fraction of your bankroll maximizes long-run growth? The formula is f = (bp − q) / b, where b is the decimal payout minus one, p is your true win probability, and q = 1 − p. Negative results mean don't bet.

Why fractional Kelly

Full Kelly is optimal only if your probability estimate is exactly right. In real betting, your number is fuzzy: books move lines, your model has variance, and small input errors compound. Quarter Kelly (0.25×) is the convention: it sacrifices a little expected growth for a much smoother bankroll curve and far less risk of ruin.

When Kelly says zero

If your true probability isn't above the implied line, Kelly recommends $0. That's not the calculator being conservative. It's telling you the bet is −EV. Pass.

Why fractional Kelly