Sports betting has the widest variance of any gambling activity — a single bad beat can wipe out weeks of profit. Kelly criterion bet sizing is the mathematically optimal way to grow a bankroll while managing risk. This calculator applies Kelly to sports bets where you have a positive edge (you've identified mispriced odds).

Enter your bankroll, the decimal odds offered, and your estimated true probability of the outcome. The calculator returns: Kelly fraction, half-Kelly, quarter-Kelly (more conservative), your expected edge per bet, and projected bankroll growth over 100 bets at that size. Use half-Kelly by default to reduce variance while keeping most of the growth.

For accumulator betting specifically: Kelly is brutally punishing because the variance is so high. A 4-fold parlay at 28/1 with 5% edge has Kelly recommending ~0.5% of bankroll per bet — meaning a £1,000 bankroll means a £5 stake. Most recreational punters bet 10–50x Kelly, which guarantees long-term ruin even with a real edge. See our parlay calculator for true parlay math.