Kelly Criterion Calculator — bet sizing without blowing up 💥
Plug in bankroll, odds, and your win probability. Get full/half/quarter Kelly, EV, and risk tags. Drop‑in single file.

Inputs

Pro tip: if your probability is the same as implied, Kelly = 0. You only bet if you have an edge.

Results

0.00%
Kelly fraction
How much of bankroll to stake at Full Kelly.
$0.00
Recommended bet
Half Kelly applied to the fraction above.
$0.00
Full Kelly
$0.00
Half Kelly
$0.00
Quarter Kelly

What is Kelly (no math headache)?

Kelly tells you how big to bet when you think you found value. Bigger edge → bigger bet. Tiny edge → tiny bet. No edge → skip. It maximizes long‑term bankroll growth while avoiding YOLO disasters.

Formula for the curious: f = (p·b − q) / b, where p is your win probability, q = 1 − p, and b is net odds (e.g., decimal odds − 1). If f is negative → don’t bet.

Expected value per $1: 0.000
Edge vs implied: 0.0%
Favorite/Underdog: —

Cheat Sheet — vibes edition

SituationEdge vibesKelly guidance
No real edgemeh0%
Small edge👶1–2% bankroll
Medium edge😎3–5%
Strong edge🔥5–10%
Trust‑me‑bro🚩Use half or quarter Kelly

Many pros chill with Half/Quarter Kelly to reduce swings, even when they believe the edge is real.

Odds help

American → implied
+150 → 100/(150+100) = 40.00%
−200 → 200/(200+100) = 66.67%
Decimal → implied
2.50 → 1/2.50 = 40.00%
Fractional → implied
5/2 → (2 / (5+2)) = 28.57%
EV per $1 = p·b − q. Kelly fraction = (p·b − q)/b. Decimal odds D → b = D − 1. American +a → b = a/100. American −a → b = 100/a.