Stake sizing & Kelly criterion calculatorHERMES TOOLS · Odds math
Fixed amount, percentage of bankroll, full / half / quarter Kelly and expected value.
Result
How it works: formula and examples
A fixed amount uses the same number every time; percentage of bankroll multiplies your current bankroll, e.g. 2% of 10000 units is 200 units. Neither changes the expected value of the bet itself.
The Kelly criterion puts your estimated win probability p and decimal odds d into f = (p×d−1)/(d−1). Put simply, it weighs your estimated edge against the possible loss to give a theoretical share of your bankroll. Half and quarter Kelly multiply that by 0.5 or 0.25.
Example: a 10000-unit bankroll, odds of 2.00 and an estimated 55% give a full-Kelly share of 10%, or 1000 units; half Kelly is 500 units and quarter Kelly 250 units. Expected net value per unit is 0.10, so the full-Kelly bet's expected net is 100 units.
If your estimate is only 45% at odds of 2.00, raw Kelly is −10% and the amount is set to zero. A wrong estimate leads to overbetting; expected value describes the average over many repeats, and any single bet can still lose the whole stake.
FAQ
Can I use the implied probability as my own estimate?
You can, but they are not the same thing; using the implied probability of the same odds usually gives a Kelly of zero.
What does a negative Kelly mean?
It means there is no positive edge under your inputs, so the tool sets the amount to zero.
Can the fixed amount exceed the bankroll?
No. The tool rejects amounts above the current bankroll, and percentages must be between 0% and 100%.
Related tools
All tools ›This tool is for math and data reference only and offers no betting services. Do not buy sports lottery tickets if you are under 18.