Bankroll Calculator
Use the Kelly Criterion to calculate optimal bet size based on your edge. Includes fractional Kelly for safer bankroll management.
Half Kelly is recommended — full Kelly is very aggressive
Unit sizing quick reference
Based on your $1,000 bankroll:
0.5u (conservative)
$5.00
1u (standard)
$10.00
2u (confident)
$20.00
3u (strong)
$30.00
5u (max play)
$50.00
What is the Kelly Criterion?
The Kelly Criterion is a formula that calculates the optimal percentage of your bankroll to wager on a bet when you have an edge. It maximises long-term growth while minimising the risk of ruin.
The formula
Kelly % = (bp − q) / b
Where b = decimal odds − 1 (the net return per $1 wagered), p = your probability of winning, q = 1 − p (probability of losing).
Why half Kelly?
Full Kelly is mathematically optimal but extremely volatile. A single bad streak can draw down your bankroll 50% or more. Half Kelly sacrifices ~25% of the theoretical growth rate but cuts variance in half. Most professional bettors use quarter to half Kelly.
Rules of thumb
- Never bet more than 5% of your bankroll on a single wager, regardless of edge.
- If Kelly says to bet 0% or negative — the bet has no value. Pass.
- Recalculate your unit size when your bankroll changes by ±20%.
- Track every bet. If your actual win rate is lower than your estimated probability, your edge estimate is wrong.
18+ only. Gambling can be addictive — play responsibly. GameSense (AGLC) · Addiction Helpline (Alberta Health Services) 1-866-332-2322 (24/7, free, confidential).