The Kelly Criterion tells you how much of your bankroll to stake based on your edge and the odds, balancing long-term growth against the risk of losing everything.

The formula is simple: stake fraction equals (odds times win probability minus one) divided by (odds minus one), but its power depends entirely on how accurate your win probability estimate is.

Most experienced bettors use fractional Kelly, typically half or quarter Kelly, because full Kelly stakes swing violently and a small error in your probability estimate can lead to dangerously large bets.

Kelly only works on bets with a genuine edge, so if the formula gives a negative number, the correct stake is zero, and no staking system can turn a losing strategy into a winning one.