How it works
Convert both prices to implied probability, add them up, then divide each by that total. The results sum to exactly 100% — the market's own view with the margin taken out.
Then what
EV% = (fair probability × offered odds − 1) × 100. A positive number means the price you found is better than the benchmark market thinks it should be.
The caveats that matter
- Splitting the margin evenly is an approximation. Bookmakers shade favourites harder, so this slightly overstates the outsider's chance.
- The answer is only as good as the market you take it from. Derive it from a soft market and you inherit its errors.
- A positive EV figure is an estimate built on an estimate, and says nothing about this particular bet — only about many of them.