The Kelly criterion and BetFTW stake bands
The Kelly criterion sizes a bet from two numbers: the probability of winning and the decimal odds. BetFTW turns the Kelly fraction into a stake score from 0 to 100 and groups picks into low, medium and high stake bands. In the 12 months to 30 October 2026, BetFTW settled 73,343 picks across the three bands.
The formula
The Kelly fraction is f = (b × p − q) ÷ b, where b is the decimal odds minus 1 (the profit per unit staked), p is the probability of winning and q = 1 − p. The result is the share of a bankroll the formula would stake. When the expected return is zero or negative, f is zero or below and the formula says not to bet.
For a 55% chance at odds of 2.10: b = 1.10, so f = (1.10 × 0.55 − 0.45) ÷ 1.10 = 0.141, or 14.1% of the bankroll. At odds of 1.80 the same probability gives f = (0.80 × 0.55 − 0.45) ÷ 0.80 = −0.0125: no bet.
Applied to a BetFTW pick
Flamengo RJ to win in Vasco Da Gama RJ vs Flamengo RJ (29 October 2026): an estimated probability of 51.0% at best recorded odds of 2.35 gives a Kelly fraction of 14.7%. BetFTW recorded a stake score of 14.7 for this pick; the two can differ slightly when the probability was updated after the best price was recorded.
From Kelly fraction to stake band
BetFTW multiplies the Kelly fraction by 100 to get a stake score. A pick is published only when the score is above 5, and no pick is published at odds above 15. Published picks fall into three bands:
| Band | Stake score | Meaning |
|---|---|---|
| Low | above 5, up to 25 | A marginal calculated edge |
| Medium | above 25, up to 50 | A clearer calculated edge at the recorded price |
| High | above 50 | A larger calculated edge at the recorded price |
A higher band means a bigger gap between the estimated probability and the price. It does not mean the pick is more likely to win: a long-priced outsider can carry a high stake score.
How each band has performed
All four sports, picks settled in the 12 months to 30 October 2026, at the best recorded odds and the recorded stake scores.
| Band | Settled picks | Hit rate | Yield |
|---|---|---|---|
| Low | 52,930 | 41.4% | +1.5% |
| Medium | 16,727 | 49.6% | +4.3% |
| High | 3,686 | 46.5% | +7.3% |
Why the full Kelly stake is aggressive
The Kelly criterion assumes the probability is exactly right. Small errors in the estimate lead to stakes that are too large, and the full Kelly stake produces deep swings even when the edge is real. Many bettors who use it stake a fraction, such as half or a quarter of the Kelly amount. BetFTW's stake score measures calculated edge; it is not advice on how much to bet.