Formula: f* = (b × p − q) / b, where b is net decimal odds, p is your win probability, q is 1−p. Full Kelly maximizes long-run growth but is extremely volatile. Quarter-Kelly is the standard in practice — smoother variance, keeps ~94% of the growth rate.
Math & probability
Kelly criterion
The mathematically optimal stake size given your edge. Most sharp bettors use a fractional version.
Example
At +120 with a 52% true win rate, full Kelly says bet 12% of bankroll — quarter-Kelly says 3%.
Related terms
Expected value (EV)
The average profit per bet if you could replay the same situation thousands of times.
Bankroll management
Sizing bets as a fixed percentage of your total wagering capital — the #1 discipline for long-term survival.
Variance
The natural swing in outcomes. Even +EV bettors lose over sample sizes of hundreds of bets.