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Kelly Criterion calculator

Turn your edge into a bet size. Enter your estimated win probability, the price, and your bankroll, and the calculator returns EV, full Kelly, fractional Kelly, and expected profit.

Inputs

Half Kelly = 50%, Quarter Kelly = 25%

Shop for a better price and see how stake and EV change.

Output

Decimal odds
1.909
American odds
-110
Expected value (EV)
5.0%
Full Kelly fraction
5.5%
Suggested stake
$13.75
Expected profit
$0.69
A positive EV of 5.0% implies an edge of 5.00 cents per dollar wagered. At 25% Kelly, the model recommends risking $13.75 from a $1000.00 bankroll.

What the Kelly criterion actually measures

The Kelly criterion answers one question: given an edge, what fraction of your bankroll should you risk to maximize long-term growth without courting ruin? It does not pick winners. It sizes bets once you have already estimated a probability of winning.

The formula is simple: f* = (bp − q) / b, where b is the net decimal odds (decimal minus 1), p is your win probability, and q = 1 − p. A positive result means you have an edge; a negative or zero result means you should not bet.

Why full Kelly is usually too aggressive
Full Kelly maximizes the theoretical geometric growth rate, but it also produces drawdowns that most bettors cannot stomach. A 50% Kelly fraction cuts peak drawdown roughly in half while surrendering only about 25% of long-run growth. Quarter Kelly is common for discretionary sports bettors who want to survive a cold month.

How to use this calculator with the live model

The Hoops PSM live model outputs a win probability for a given total or spread. Plug that probability into the calculator, enter the live price your sportsbook is offering, and set your Kelly fraction. The calculator returns the stake that keeps your bankroll growth optimal while respecting your risk tolerance.

  • Win probability: from the model's cover-probability or over/under projection.
  • Odds: the price you can actually bet right now, not the closing line you hope to get.
  • Bankroll: the amount you are willing to lose without changing your lifestyle.
  • Kelly fraction: your personal risk dial. Start conservative.

Common mistakes

The most expensive error is overestimating your edge. If you think a team covers 58% when the true probability is 52%, Kelly will happily tell you to bet the house — and the house will take it. Be honest with your probability inputs. The second most common mistake is chasing a losing day by raising the Kelly fraction. The math does not care about your mood.

Another trap is ignoring correlation. If you have three live bets running on the same game, your effective exposure is much larger than three separate Kelly stakes suggest. Treat correlated positions as one combined wager when sizing.

When not to bet

If the calculator returns zero or negative EV, the price is fair or worse. No bet is a bet. In live markets, the best trades are often the ones you skip. The model's green-light gates exist precisely because most in-game windows do not offer enough edge to justify risk.

Try it inside the model

The calculator uses the same Kelly math that powers the stake recommendations inside the live model. Use it here for quick estimates, or sign up to run the full projection engine.