Definition
Kelly staking aims to maximize long-term bankroll growth by sizing bets in proportion to the edge you believe you have. Bigger edge, bigger stake. Smaller edge, smaller stake.
Why bettors use fractional Kelly
Full Kelly can be volatile, especially when your probability estimates are imperfect. That is why many serious bettors use half-Kelly or quarter-Kelly instead.
When Kelly helps
- You have a consistent process for estimating true probability.
- You want a structured link between edge and position size.
- You want to avoid arbitrary staking decisions.
When Kelly can fail
Kelly depends on your probability estimate being reasonably accurate. If your model is overconfident, the formula can recommend stakes that are too large.
Related terms
- Bankroll defines the capital Kelly is working with.
- Expected value determines whether there is any real edge to size in the first place.