No-vig fair odds are what a set of betting odds implies once the bookmaker’s margin has been removed. Raw odds always overstate the probabilities, because the two sides are shaded to sum above 100%; the no-vig version rescales them back to a true 100%, revealing the market’s honest estimate of each outcome. It is one of the most useful calculations a bettor can know, and it is the natural sequel to understanding implied probability and the vig.
What no-vig fair odds are
Think of the overround as padding spread across both outcomes. The no-vig fair odds ask a simple question: if this market summed to exactly 100% instead of 107%, what would each side’s probability be? The answer is the market’s fair probability — the closest thing you can extract to what the odds-setter really believes, stripped of the house edge. On a prediction-market exchange the price is already close to this figure, which is part of why exchange prices and no-vig fair odds are useful to compare directly.
How to calculate them
For a standard two-way market the method is straightforward normalisation:
- Convert both sides to implied probabilities.
- Add them together to get the total (the overround — more than 100%).
- Divide each side’s implied probability by that total.
The two results now sum to 100% and are your no-vig fair probabilities. The no-vig calculator performs exactly this, and the odds converter helps with the first step.
A worked example
Take a market where one side implies 55% and the other 52%, a total of 107%. Divide each by 1.07: the first becomes 55 ÷ 107 = 51.4%, the second 52 ÷ 107 = 48.6%. Those two now add to 100%, and 51.4% is the fair probability the market implies for the first outcome once the roughly seven-point margin is removed. Before the adjustment you would have overpaid for that side; after it, you know the real number to test your own view against.
Comparing across venues
No-vig fair odds are what make a sportsbook line and a prediction-market price comparable. A sportsbook quote carries a margin; an event-contract price is already close to margin-free. By converting the sportsbook line to its no-vig fair probability, you put both on the same footing and can see which venue offers the better deal on the same outcome — a habit that ties directly into prediction markets versus sports betting and to hunting for value across platforms.
Limits of the method
Simple normalisation assumes the margin is spread proportionally across the outcomes, which is a reasonable approximation but not always exact — some books load more vig onto favourites or longshots. Multi-way markets (three or more outcomes) need the same idea applied across every outcome and are messier to compute by hand. And no-vig fair odds tell you what the market thinks, not what is correct; they are a cleaned-up benchmark to measure your own expected-value judgements against, not a guarantee. Used with that caveat, they are one of the sharpest tools in a trader’s kit.
Frequently asked questions
What are no-vig fair odds?
No-vig fair odds are the probabilities a set of betting odds implies once the bookmaker’s margin is removed and the two sides are rescaled to sum to 100%. They reveal the market’s true estimate of each outcome, stripped of the house edge.
How do you remove the vig from odds?
For a two-way market, convert both sides to implied probabilities, add them to get the total (over 100%), then divide each side by that total. If the sides imply 55% and 52% (107% total), the no-vig fair odds are 51.4% and 48.6%.
Why compare sportsbook odds to prediction-market prices using no-vig odds?
Because a sportsbook line includes a margin while an event-contract price is already close to margin-free. Converting the sportsbook line to its no-vig fair probability puts both on the same footing, so you can see which venue offers the better price on the same outcome.