Odds guide
Implied probability and the margin
Why the probabilities in a posted market add up to more than 100%, and what to do about it.
1. Convert every outcome
Turn each posted price in the market into an implied probability. Include every outcome, including draws and ties, or the total will be wrong.
2. Sum them
Add the implied probabilities. The amount above 100% is the overround — the venue's theoretical margin on balanced action.
3. Normalise proportionally
Divide each implied probability by the total. The results sum to 100% and are the market's margin-adjusted probabilities. Proportional normalisation is the convention used throughout this platform.
4. State the method
Alternative removal methods, such as shin or logarithmic approaches, distribute margin differently and produce different figures. Any published no-vig number should name the method used to produce it.
Sources
- Source: SportsWager editorial desk
Last reviewed: 2026-08-01