Direct Answer
Bet sizing is the decision of how much of your bankroll to risk on each wager. The right answer depends on edge, variance, correlation, and confidence in the estimate itself — and is almost always smaller than feel suggests.
Key Takeaways
- Flat is the default; scaled is an upgrade, not a starting point.
- Use fractional Kelly, never full Kelly.
- Cap maximum bet to protect against estimate error.
- Upsize on price, not on conviction.
Flat vs scaled sizing
Flat sizing (every bet the same %) is the safest default and the hardest to manipulate emotionally. Scaled sizing (units by confidence tier) can capture more EV when edge is reliably estimated, but it requires honest self-calibration and a hard cap.
Why Kelly is too aggressive in practice
Full Kelly maximizes long-run growth assuming exact knowledge of edge. Real edges are uncertain. Fractional Kelly (¼–½) recovers most of the growth with a fraction of the volatility — and survives estimation error that would bankrupt full-Kelly bettors.
Confidence is not edge
Feeling sure about a bet is not the same as having a larger edge. Most amateurs upsize on conviction; most professionals upsize on price (only when the number is uniquely off-market).
Frequently asked questions
Should I bet more on stronger plays?+
Only if your strongest plays have historically produced larger CLV. If not, you are sizing by feel — which is noise.
Educational only. Not wagering, financial, or legal advice. See our editorial policy.