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Edge & sizing · free · runs in your browser

Kelly Criterion Calculator

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.

Suggested stake · ¼ Kelly$13.751.38% of bankroll · full Kelly 5.50%

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

The Scout’s Notebook

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

  1. Enter bankroll, probability, and price. The fair probability should come from a devigged market or a model you trust.
  2. Pick a fraction. Quarter Kelly is the standard; full Kelly is the theoretical ceiling.
  3. 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.