Kelly Criterion Calculator

Formatting only. This does not change the calculation.
American (+150, -110), decimal (2.50), fractional (3/2) or a probability (40%).
Leave on automatic unless a bare number is ambiguous.
Kelly staking needs your own estimate, not the bookmaker's implied probability.
Multiply full Kelly by this. Half Kelly (0.5) keeps most of the growth with far less variance.
Kelly stake
100
Betting Odds Calculator
Decimal odds
2
American / moneyline odds
100
Fractional odds
1/1
Implied probability
50 %
Hong Kong odds
1
Indonesian odds
1
Malay odds
1
Profit if the bet wins
100
Total return (stake plus profit)
200
Kelly fraction of bankroll
0.1
Edge (expected profit per unit staked)
0.1
Expected value of the bet
10
Break-even win probability
50 %
Worked out from Kelly, J.L. Jr (1956), "A New Interpretation of Information Rate", Bell System Technical Journal 35(4), 917-926 and 3 other sources.
Kelly assumes your probability estimate is correct. Overestimating the edge overbets badly, which is why most practitioners use half Kelly or less.
This is an arithmetic tool, not betting advice. Bookmaker prices already carry a margin, so the long-run expected value of a bet at posted odds is negative unless you genuinely have an edge. Gamble only what you can afford to lose.

How this is worked out

6 steps
  1. Decimal price = 2, i.e. 100 American, 1/1 fractional, 50% implied.
  2. A stake of 100 returns 200 in total, a profit of 100.
  3. b = decimal - 1 = 1, p = 0.55, q = 0.45.
  4. f* = (bp - q)/b = (0.55 - 0.45) / 1 = 0.1
  5. Full Kelly stakes 10% of the bankroll: 100.
  6. The break-even probability at this price is 50%, so the edge is 0.1 per unit staked.

Results are general information, not financial, tax, legal, medical or engineering advice.