A no-vig estimate adjusts quoted implied probabilities to remove a market overround under a stated allocation method.
The two-step method
A no-vig price estimates what the odds would be without the book’s margin. For a two-way market:
- Convert each side to implied probability.
- Divide each probability by the total of both.
For a −110/−110 spread, both sides imply 52.38%, a total of 104.76%, so each becomes 52.38 ÷ 104.76 = 50%. For a −150/+130 moneyline, the sides imply 60.00% and 43.48%, a total of 103.48%. Dividing gives 57.98% and 42.02%, which add up to exactly 100%.
Turn a fair probability into fair odds
A probability of 50% or more converts to American odds of −100 × p ÷ (1 − p); below 50%, use +100 × (1 − p) ÷ p. In decimal, fair odds are 1 ÷ p. The −150/+130 market therefore has fair prices of about −138 and +138, or 1.72 and 2.38 in decimal.
The no-vig fair odds calculator runs this conversion for both sides of any two-way market.
Use the fair price as a benchmark
A fair price is most useful when another book offers something better. If the underdog in that market is available at +145 elsewhere, the expected return against the fair estimate is 0.4202 × 2.45 − 1 = +2.9% of the stake. If the best available price is +135, the same calculation gives −1.3%: below fair, even though it beats the +130 at the first book.
The reference is only as good as the market it comes from. A widely bet main line with high limits makes a better reference than a low-limit market few people have tested.
The assumption behind the division
Dividing proportionally assumes the margin is spread across outcomes in proportion to their probabilities. Books don’t necessarily price that way, and other methods give different answers. The additive method subtracts an equal share of the excess from each side; the power method raises each side to the same power, chosen so the results sum to 100%. For the same −150/+130 market:
| Method | Favorite | Underdog |
|---|---|---|
| Proportional | 57.98% | 42.02% |
| Additive | 58.26% | 41.74% |
| Power | 58.40% | 41.60% |
The additive and power methods place more of the margin on the underdog, consistent with the favorite-longshot bias. In balanced markets near −110/−110, every method returns 50/50; the differences grow with lopsided prices and with markets that have many outcomes. Whichever method you use, use it consistently and note it in your records.
More outcomes, and markets with one side
The same method works for more than two outcomes. A soccer market at home 2.40, draw 3.30, and away 3.10 implies 41.67%, 30.30%, and 32.26%, a total of 104.23%. Dividing through gives 39.98%, 29.07%, and 30.95%.
Be careful with markets where only one side is offered, such as many milestone props. With no opposing price there is nothing to normalize against, and treating the quoted price as fair overstates the probability by the full margin.
Does this topic predict the next result?
No. A definition, historical statistic, market price, or model output is not a guarantee. Treat estimates as conditional on their data and assumptions, and keep the uncertainty visible.