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Kelly Criterion

Kelly Criterion Betting Calculator – find the mathematically optimal stake for every +EV wager

What is the Kelly Criterion?

The Kelly Criterion is a bankroll‑management formula that tells you exactly what fraction of your roll to risk on a positive‑expected‑value (+EV) bet.

  • Maximises long‑term bankroll growth.
  • Protects you from over‑staking and potential ruin.
  • Can be scaled down (Half‑Kelly, Quarter‑Kelly, etc.) to smooth short‑term variance.

Inputs and outputs

  • Odds – decimal format (e.g. 2.20).
  • Win probability – your calculated chance of success (e.g. 60 %).
  • Kelly multiplier – Full, Half, Quarter or a custom fraction.
  • Result – stake shown as a percentage of bankroll and as a currency amount.

Example – Odds = 2.20, win probability = 60 %

  1. Edge = (win probability × odds) − 1 → (0.60 × 2.20) − 1 = 0.32
  2. Kelly fraction = edge ÷ (odds − 1) → 0.32 ÷ 1.20 = 0.2667 (≈ 26.67 %)
  3. With a 5 000 $ bankroll, Full‑Kelly stake = 0.2667 × 5 000 $ = 1 333.33 $

Why use a Kelly staking plan?

  1. Maximum geometric growth – proven to deliver the highest compounded return over many bets.
  2. Automatic risk control – stake shrinks as your edge narrows or bankroll falls.
  3. Objective discipline – removes emotion from stake sizing.
  4. Adjustable aggression – Half‑ or Quarter‑Kelly reduces volatility if edge estimates are uncertain.

How to use the calculator

  1. Enter the market odds in decimal form.
  2. Input your true win probability, derived from models or research.
  3. Choose a Kelly multiplier (Full for maximum growth, fractional for lower variance).
  4. Read the recommended stake (percentage and currency).
  5. Place the bet only if the stake feels comfortable for your risk tolerance.

Tip: Track your actual stakes versus Kelly stakes over time; if draw‑downs feel too steep, move from Full to Half‑Kelly.

The Kelly formula in plain English

Fraction to bet = ((odds × win probability) − 1) divided by (odds − 1).

Stake = fraction × bankroll.

For fractional Kelly, multiply the fraction by 0.5 for Half‑Kelly, 0.25 for Quarter‑Kelly, and so on.
If your odds are in American or fractional format, convert them to decimal first with the Odds Converter.

Frequently asked questions

Is Kelly always better than flat staking?
Over the long run, yes—if your edge estimates are accurate. Flat staking is simpler but grows the bankroll more slowly.

What if my probability estimate is wrong?
Kelly assumes perfect edge estimation. Over‑estimating edge means over‑betting. Using Half‑ or Quarter‑Kelly cushions the impact of estimation error.

Can I apply Kelly to parlays or multiples?
Yes. Calculate the combined decimal odds and combined probability, then feed those into the calculator.

How often should I recalculate Kelly stakes?
After each bet if your bankroll has changed, or whenever your edge estimate updates.