Free Tool

Kelly Criterion Calculator

Find the optimal bet size for your edge. Enter your estimated win probability and the odds. Kelly handles the rest.

📐Full / Half / Quarter Kelly
🎯Edge detection
💰Dollar bet size

Bet Odds

Your Estimated Win Probability

Book implies 52.4%
%

✓ Edge: +2.6% above implied probability

Bankroll

$

Kelly Fraction

Kelly Result

Recommended Bet

$55

5.5% of bankroll

Full Kelly %5.5%
Full Kelly %5.5%
Expected Value5.00¢ per $1
Your Edge+2.6%

Most professionals use Quarter or Half Kelly to reduce variance. Full Kelly maximizes growth but causes large swings.

The Formula

How Kelly Criterion Works

  1. 01

    Estimate your true win probability

    This is the hard part. Be honest. Most bettors overestimate their edge. Compare to the implied probability from the odds.

  2. 02

    Calculate your edge

    Edge = your probability − implied probability. At -110, implied is 52.4%. If you estimate 57%, your edge is 4.6%.

  3. 03

    Apply the formula

    f* = (bp − q) / b, where b = net odds, p = win probability, q = loss probability (1−p). This is your optimal bet fraction.

  4. 04

    Use fractional Kelly

    Full Kelly maximizes growth but creates wild swings. Most pros use half or quarter Kelly for smoother results.

Read more: Kelly Criterion definition · Bankroll Management Guide

Quick reference

Kelly by Edge Size

Your EdgeOddsFull KellyHalf Kelly
+2%-1104.2%2.1%
+5%-11010.5%5.25%
+10%-11021%10.5%
+5%+1508.3%4.17%
+10%+20015%7.5%

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