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Kelly stake calculator
This calculator will work out how much you need to stake, based on the Kelly Criterion, if you input your bankroll, the odds available and your estimated probability that the bet will win. The idea behind it is to optimise your returns from betting, taking account of value, risk and the money you have available. It has the effect of increasing your stakes as your bank grows or reducing stakes if you have a bad run of losses.
Notes for using this calculator
- Complete all the white boxes
- Odds are in decimal format
- Commission rate is zero by default and only needs changing if you're using a betting exchange that deducts commission from your profit
- Implied odds are based on the win probability you provide
- Value index – value exists if this number is above 100
- If the stake is negative you should not place the bet but you could consider laying the bet if you are able to lay at the odds you have entered
Kelly is just one way of determining how much you should stake but there is no right formula. Please be aware that the results are heavily geared to the win probability so you need to be confident in the accuracy of your estimations.
The theory of Kelly applies to events with only two outcomes but is regularly adopted for three outcome events such as football 1X2 match betting. Many people modify the formula for their purposes, often making it more conservative to reflect the potential for inaccuracies when estimating win probabilities. A popular approach is to bet half the Kelly suggested stake, which significantly reduces risk to bankroll without such a significant reduction in the profitability of the system.
The formula
The Kelly formula is:
Stake £ = ((Odds – 1) x Prob – (1 – Prob)) / (Odds – 1) x Bank
Where, based on the names used for the calculator...
- Odds are Actual odds
- Prob is Win probability %
- Bank is Betting bank
Actual odds = (Odds available – 1) x (1 – Commission rate) + 1
Implied odds = 1 / Win probability
Value index = Actual odds / Implied odds
Remember: in any calculations involving a percentage, the percentage is expressed as a fraction of 1 (i.e. 25% is 0.25).
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