Overround
The total of a market's implied probabilities above 100%, the standard way to express a bookmaker's margin on multi-outcome markets.
Overround (book percentage) adds up the implied probabilities of every outcome in a market. A fair book sums to 100%. Anything above that is margin.
Soccer 1X2 example
Illustrative prices: home 2.10, draw 3.40, away 3.60.
| Outcome | Odds | Implied |
|---|---|---|
| Home | 2.10 | 47.62% |
| Draw | 3.40 | 29.41% |
| Away | 3.60 | 27.78% |
| Sum | 104.81% |
- Overround: 4.81%.
- Payout rate (theoretical return): 1/1.0481 = 95.41%.
- Bookmaker margin as a share of stakes: 4.59%.
Overround and vig are not the same number: 4.81% versus 4.59% here. Overround is measured against 100% of probability; vig against the total staked.
Why it scales with outcomes
The more outcomes a market has, the more room there is for margin. A two-way handicap might run at 103% to 105%; correct score markets and outright winners commonly run far higher.
Using it
Compare the overround on the same fixture across bookmakers to find the most efficient price. Note that the overround is rarely spread evenly: longshots tend to carry more of it than favourites.