Informational bankroll math
KELLY CRITERION
CALCULATOR
Enter win probability and odds to calculate full Kelly, half Kelly, and quarter Kelly fractions. This is informational math, not betting advice or a recommendation to wager.
THE FORMULA
The Kelly criterion uses decimal odds d, profit odds b = d - 1, win probability p, and loss probability q = 1 - p. The formula is f* = (b*p - q) / b. If f* is less than or equal to zero, there is no positive edge by the formula and Kelly suggests no allocation.
FRACTIONAL KELLY
Full Kelly is mathematically aggressive because it assumes the probability estimate is correct. Many practitioners study fractional Kelly instead, such as half Kelly or quarter Kelly, because model probabilities are estimates and can be wrong.
WORKED EXAMPLE
At +100 odds, decimal odds are 2.00 and b = 1. If your estimated win probability is 55%, then q = 45% and f* = (1 * 0.55 - 0.45) / 1 = 0.10. Full Kelly is 10% of bankroll, half Kelly is 5%, and quarter Kelly is 2.5%. These are informational fractions, not instructions to wager.
HOW WINFORGE FITS
WinForge outputs a model probability and edge for each projection when market lines are available. You can use the EV calculator for expected-value math, the no-vig calculator for fair probability, and how WinForge works for the projection workflow.
RESPONSIBLE USE
This is an informational math tool, not betting advice or a recommendation to wager. Model probabilities are estimates and can be wrong. WinForge is not a sportsbook. 21+ where required. If you or someone you know has a gambling problem, call 1-800-GAMBLER.
FREQUENTLY ASKED QUESTIONS
What is the Kelly criterion?
The Kelly criterion is a bankroll math formula that estimates what fraction of bankroll would maximize long-run growth if your win probability estimate and payout odds are correct.
What is fractional Kelly?
Fractional Kelly uses a smaller fraction of the full Kelly result, commonly half Kelly or quarter Kelly, because probability estimates are uncertain and full Kelly can be volatile.
Should I use full Kelly?
Most practitioners use fractional Kelly rather than full Kelly. This calculator is informational math only, not betting advice or a recommendation to wager.