Find the mathematically optimal stake for a positive-EV bet.
Arbitrage Calculator
Find guaranteed profit opportunities across two bookmakers.
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ARB FOUND
Stake on Outcome 1
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Stake on Outcome 2
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Guaranteed Profit
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ROI
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Back & Lay Calculator
Calculate lay stakes for Betfair exchange hedging. Back at a bookmaker, lay on the exchange.
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%
Lay Stake
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Profit if Back Wins
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Profit if Lay Wins
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Betfair Liability
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Bonus Bet Turnover Calculator
Convert bonus/free bets into guaranteed cash. Bonus bet stake is not returned — only profit.
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%
Lay Stake
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Guaranteed Profit
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Retention %
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Betfair Liability
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No Vig / Fair Odds Calculator
Remove the bookmaker's margin to find true fair odds and probabilities.
Fair Odds 1
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Fair Odds 2
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Fair Odds 3
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True Prob 1
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True Prob 2
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True Prob 3
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Overround
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Vig / Margin
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Vig Calculator
See exactly how much the bookmaker is taking from both sides of a two-way market.
Bookmaker's Edge
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Vig / Margin
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Overround
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Fair Odds 1
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Fair Odds 2
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Implied Prob 1
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Implied Prob 2
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True Prob 1
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True Prob 2
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Kelly Criterion Calculator
Determine optimal bet sizing based on your edge and bankroll.
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$
+EV BET
Full Kelly %
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Recommended Stake
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Expected Value / Bet
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Edge %
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Conservative Sizing
Quarter Kelly
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Half Kelly
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Full Kelly
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Expected Value Calculator
Determine whether a bet has positive expected value (+EV).
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+EV BET
Expected Value
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EV % per Bet
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Break-even Probability
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Your Edge
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Odds Converter
Enter odds in any format — decimal (2.50), fractional (3/2), or American (+150 / -200).
Decimal
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Fractional
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American
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Implied Probability
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Common Odds Reference
Decimal
Fractional
American
Implied Prob.
1.50
1/2
-200
66.67%
1.80
4/5
-125
55.56%
1.91
10/11
-110
52.36%
2.00
1/1
+100
50.00%
2.50
3/2
+150
40.00%
3.00
2/1
+200
33.33%
4.00
3/1
+300
25.00%
5.00
4/1
+400
20.00%
10.00
9/1
+900
10.00%
21.00
20/1
+2000
4.76%
Hedge / Cash Out Calculator
Lock in a guaranteed profit on an existing bet by hedging the opposite outcome.
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Hedge Stake
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Profit if Original Wins
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Profit if Hedge Wins
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Guaranteed Profit
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The Kelly Criterion sets your stake to maximise the long-run growth of your bankroll given an edge. Enter the odds and your estimate of the true probability, and the calculator returns the optimal fraction of your bankroll to stake.
How to use it
Enter the decimal odds on offer.
Enter your estimated fair probability of the outcome (from a no-vig line).
Enter your bankroll.
Read the full-Kelly stake, and the safer half and quarter-Kelly amounts.
Worked example. Odds of 2.10 with an estimated true probability of 52% gives an edge, and full Kelly suggests staking about 7.6% of bankroll. Many bettors use half-Kelly (about 3.8%) to cut variance while keeping most of the growth.
Kelly only works when the bet genuinely has positive expected value, so pair it with the EV calculator and read the +EV guide. Overestimating your edge is the most common mistake.
Frequently asked questions
Should I use full Kelly?
Most disciplined bettors use half or quarter Kelly. Full Kelly maximises growth in theory but assumes your probability estimate is exact, and real edges are uncertain, so fractional Kelly reduces the risk of large drawdowns.
What probability do I enter?
Use your best estimate of the true probability, ideally a no-vig fair probability derived from a sharp market rather than the bookmaker's own implied probability.
What if Kelly returns zero or a negative stake?
That means the bet has no edge at the odds and probability you entered. Kelly only recommends a stake on a positive-EV bet.