Kelly Criterion vs Flat Betting: Which Staking Plan Wins?
Flat betting risks the same amount every bet; Kelly sizes each bet to your estimated edge. Kelly maximizes long-run growth in theory, but it punishes overestimated edges brutally in practice.
Kelly Criterion
Bets a bankroll fraction proportional to your edge: f = (bp - q) / b.
Pros
- Mathematically maximizes long-term growth
- Automatically scales with edge size
- Compounds wins efficiently
Cons
- Punishes overestimated edges severely
- Huge swings - 50%+ drawdowns are normal
- Requires accurate win probability estimates
Flat Betting
Risks a fixed unit (typically 1-2% of bankroll) on every bet regardless of edge.
Pros
- Simple and immune to estimation error
- Small, predictable drawdowns
- Easy to track performance in units
Cons
- Leaves growth on the table with big edges
- Doesn't adapt to bet quality
- Unit needs periodic recalculation
The Verdict
Most bettors should flat bet 1-2% of bankroll, or use quarter-to-half Kelly at most. Full Kelly is only optimal when your probability estimates are accurate - and almost nobody's are.
Frequently Asked Questions
Is Kelly betting too risky?
Full Kelly produces drawdowns most bettors can't stomach - a 50% bankroll drop is expected. Half Kelly keeps about 75% of the growth with half the volatility, which is why practitioners rarely bet full Kelly.
What win rate do I need for flat betting to profit?
At standard -110 odds you need 52.38% to break even. A flat bettor winning 55% earns about 5% ROI per bet - excellent by professional standards.