You have an edge. How much of your bankroll do you wager? Bet too much and a bad streak wipes you out. Bet too little and you're not growing.
In 1956 at Bell Labs, John L. Kelly Jr. derived the optimal answer:
f* = (b × p − q) / b
b = decimal odds − 1 · p = win prob · q = 1 − p
This gives the fraction of your bankroll that maximizes long-run growth rate.
🎮 Kelly Calculator
Full Kelly
--%
$0
Half Kelly
--%
$0
Quarter Kelly
--%
$0
Flat 1%
1.0%
$10
⚠️ Negative Kelly fraction — this bet has no edge. DON'T BET.
Why fractional Kelly: Wharton research showed full Kelly leads to bankruptcy in nearly 100% of simulations when you misestimate win probability by even 5%. Half Kelly: also ruin. Quarter Kelly: profitable. Our default ($10 flat ≈ 1% of $1000 bankroll) is approximately quarter Kelly for typical Rank-1 picks.
📊 Bankroll Growth Simulation
100 bets at the win probability + odds you set above. 4 strategies: flat $10/bet, Quarter Kelly, Half Kelly, Full Kelly. Same wins/losses for each strategy (same RNG seed) so you can compare.
Flat $10 Quarter Kelly Half Kelly Full Kelly
Starting bankroll: $1000. 100 bets. Same simulated outcomes across all 4 strategies.