Free tool
Kelly Criterion Calculator
The Kelly formula tells you the mathematically optimal stake for a given edge. Full-Kelly maximizes growth but swings hard — most sharp bettors use quarter-Kelly.
%
$
Kelly fraction
Quarter-Kelly is the standard for real bettors — smoother variance, still captures most of the growth.
Recommended stake
$87.50
4.38% of bankroll
Breakdown
Decimal odds2.200
Implied win %45.5%
Your edge+9.5 pts
Full Kelly17.50%
The formula
f* = (b × p − q) / b
Where b is decimal odds minus one (net return per dollar), p is your win probability, and q = 1 − p.
Why fractional Kelly? Full Kelly assumes your win probability is exactly right. In practice, you are estimating — and estimation error gets punished quadratically by full Kelly. Quarter-Kelly cuts variance by ~75% while keeping ~94% of the long-run growth rate.
If Kelly returns negative, it means the bet has no edge and you should pass.