Kelly Criterion Calculator

How much to stake—

Give a bankroll, a probability and a price and this becomes the stake the edge supports.

Bankroll

Fair win probability

Your price

↑ Break-even 52.4%Edge +2.6 pts ↑

Kelly fraction

Full Kelly$55.005.50% of the roll

Edge+2.6 ptsbreak-even 52.4%

Growth / bet+0.06%expected log growth

To win$12.50profit if it lands

Expected log growth by fractionPast 1.00× you add variance and subtract growth

Full Kelly assumes your probability is exact — it never is. Fractional Kelly trades a little growth for a lot less ruin, which is why ¼–½ is the standard.

Show the math

f* = (b·p − q) / b, b = decimal − 1b = 0.9091, p = 0.5500 → f* = 5.50%

stake = bankroll × f* × 0.25$1,000.00 × … = $13.75

Send this calculation

Your numbers travel in the link — whoever opens it sees this exact calculation.

KeyboardUp and down arrows step any price — 5 cents on an American number, a hundredth on a decimal. Enter moves to the next field. Slash jumps back to the first one from anywhere on the page.

What this will not claimFull Kelly assumes your probability is exact. It never is, which is why the quarter and half fractions exist and why this page defaults to a quarter.

Related calculators

Expected Value CalculatorYour price vs the fair probability — EV%, fair odds, and the Kelly-suggested stake.No-Vig Fair Odds CalculatorStrip the book's margin from a two-sided market — three devig methods side by side.Parlay CalculatorCombined odds, payout, and — with per-leg fair probabilities — the parlay's true EV.All 13 calculators →

How does the Kelly criterion size a bet?

The Kelly criterion stakes a fixed fraction of bankroll equal to (b·p − q)/b — where b is the net decimal payout, p the fair win probability, and q = 1 − p — the mathematically optimal size for long-run bankroll growth.

How it works & common questions

The calculator shares the desk bankroll used across the betting suite, so a stake sized here matches the ledgers everywhere else.

How it works

Enter bankroll, probability, and price. The fair probability should come from a devigged market or a model you trust.
Pick a fraction. Quarter Kelly is the standard; full Kelly is the theoretical ceiling.
Read the stake. Dollars and percent of bankroll — zero when there is no edge at the price.

Why bet fractional Kelly instead of full Kelly?

Because Kelly's optimality assumes your win probability is exactly right, and an overestimated edge makes full Kelly overbet aggressively. Betting a quarter or half of the Kelly fraction sacrifices a small amount of growth for a large reduction in variance and risk of ruin.

Learn more: Kelly Staking (guide)

Dynatyze Betting is analytics and education for people 21 and over. It is not a sportsbook: no wager is ever placed on Dynatyze — the tools help you find and price the best available bet elsewhere. If gambling stops being fun, help is free and confidential at 1-800-GAMBLER.