Kelly criterion calculator (full and fractional)

A Kelly criterion calculator turns the odds and your estimated win probability into a stake: the fraction of your bankroll that maximizes long-run growth if that probability is right. Enter both below. Because estimates are rarely exact, the calculator defaults to half Kelly, which keeps most of the growth with far less risk.

Kelly criterion calculator

Enter the price and your own estimate of the win probability. The result is only as good as that estimate.

Odds format

Odds offered

Your win probability

Your estimate, e.g. from a no-vig line

Bankroll

Kelly fraction

Suggested stake: $27.50; 2.75% of bankroll
Full Kelly: 5.50%; of bankroll
Your estimated edge: +5.00%; Expected value per unit staked
Long-run growth kept: 75%; vs full Kelly, if your probability is right

Assumptions and limitations

Kelly fraction f = (b·p − q) ÷ b, where b is the net odds (decimal odds − 1), p your win probability and q = 1 − p. Equivalently, edge ÷ net odds.
It assumes your probability is correct. If you overestimate it, Kelly overbets, and betting more than the true Kelly amount adds risk while lowering long-run growth. That is the usual reason to bet a fraction of Kelly.
It treats each bet as independent and the bankroll as divisible, and it maximizes growth over many bets. It does not prevent losing streaks; even a correct Kelly bettor can lose a large share of the bankroll.
Simultaneous bets, sportsbook stake limits and maximum bets aren't modeled.
Nothing you enter is stored or sent anywhere.

How the Kelly criterion calculator works

The calculator uses the standard two-outcome Kelly formula: stake fraction = (b × p − q) ÷ b, where b is the net odds (decimal odds − 1), p your win probability and q = 1 − p. That's the edge divided by the net odds.^[1] A negative result means the bet has no edge at your probability, so the suggested stake is zero.

The "long-run growth kept" figure compares the expected log growth of the fraction you chose with full Kelly. Half Kelly typically keeps about three-quarters of the growth at half the stake.

Before you use the number

Your probability is an estimate. Overestimate it and Kelly overbets; betting more than the true Kelly amount adds risk and lowers growth.^[1] That's why the default here is half Kelly.
Kelly is for the long run. It can be very risky in the short term, and no staking rule guarantees a profit over a finite run of bets.^[1]
One bet at a time. It doesn't handle several simultaneous or correlated bets.

For the full explanation, with worked examples, read Kelly criterion betting: what it assumes and how it fails.

Frequently asked questions

How do I calculate a Kelly stake?

Convert the odds to decimal, subtract 1 to get the net odds b, then compute (b × p − q) ÷ b, where p is your win probability and q = 1 − p. Multiply by your bankroll for the stake.

Should I use full Kelly or half Kelly?

Half Kelly is the common choice when your probability is an estimate. It keeps about three-quarters of full Kelly's long-run growth (if your estimate is right) at half the stake, and it is far less damaging if you overestimate your edge.

Why does the calculator say no bet?

Because at your probability the bet's expected value is zero or negative, so the Kelly fraction is zero or below.

Kelly criterion calculator