Question 1

What is the Kelly Criterion in sports betting?

Accepted Answer

The Kelly Criterion is a formula for sizing bets that maximizes a bankroll's long-run growth rate given your edge and the odds offered: f = (bp − q) / b.

Question 2

What is the Kelly Criterion formula?

Accepted Answer

Kelly fraction f = (bp − q) / b, where b is the decimal payout odds minus 1, p is your true win probability, and q is 1 − p. The result is the percentage of your bankroll to wager on that specific bet.

Question 3

Why do bettors use fractional Kelly instead of full Kelly?

Accepted Answer

Full Kelly assumes your probability estimate is exactly correct, which it never is in practice. Betting a fraction of full Kelly — commonly 25% (quarter-Kelly) or 50% (half-Kelly) — trades some theoretical growth rate for much lower variance, protecting the bankroll against estimation error.

Question 4

What happens if you bet more than your Kelly fraction?

Accepted Answer

Overbetting past full Kelly increases variance faster than it increases expected growth, and betting roughly double the Kelly fraction or more actually reduces long-run bankroll growth toward zero — it's mathematically the same as gambling with no edge at all, despite still having a real edge on the bet.

The Kelly Criterion for Bet Sizing | ChalkPicks