Expected value in one line
EV% = your chance × decimal odds minus 1. At odds of 2.50 and a 45% chance: 0.45 × 2.50 minus 1 = 12.5%. On average, each ₦1,000 staked on bets like this returns ₦125 profit. The expected value calculator does the sum.
Where chance estimates come from
- Fair oddsRemove the margin from a sharp market with the margin calculator and compare with a softer bookmaker's price.
- Your own recordsA model or a long, honest record of your picks by type and price.
- Not hunchesA feeling that a team "must win" is not an estimate. If you cannot explain the number, do not bet on it.
The Kelly criterion
Kelly share of bankroll = (chance × odds minus 1) ÷ (odds minus 1). With ₦50,000, odds 2.20 and a 50% chance, full Kelly is 8.33%, a ₦4,167 stake. The Kelly calculator shows full, half and quarter Kelly.
Why fractions of Kelly
| Version | Growth if estimates are right | Swings | Damage if estimates are too high |
|---|---|---|---|
| Full Kelly | Highest | Large | Severe |
| Half Kelly | About three quarters of full | Much smaller | Limited |
| Quarter Kelly | Lower | Small | Small |
Most estimates are a little optimistic. Half or quarter Kelly protects your bankroll from that.
Positive EV does not stop losing runs. Ten losses in a row are normal over a season of bets at 2.50.
Questions
How do I know if my estimates are good?
Record every bet with the odds and your estimate. After a few hundred bets, compare your average estimate with the actual win rate.
Is a favourite ever value?
Yes. Value is about price against chance, not about short or long odds.
Can I combine value bets in an acca?
Yes, the EV compounds, but so does the risk, and the chance estimate gets harder.