Betting maths guide
What Are No-Vig Fair Odds?
No-vig fair odds are an estimate of what the odds might look like after removing bookmaker margin from a market. They help explain prices, but they do not automatically show that a bet is good value.
What vig means
Vig, margin, juice and overround are different ways to talk about the edge built into betting odds. In a balanced market without margin, the probabilities of all outcomes would add up to about 100%.
Bookmaker prices often add up to more than 100%. The amount above 100% is one way to understand the built-in margin.
Implied probability and book percentage
Decimal odds can be converted into implied probability by dividing 1 by the odds. For example, decimal odds of 2.00 imply 50% before any margin or other market factors are considered.
In a two-outcome market, you can add both implied probabilities together. If they add up to more than 100%, the market has an overround.
No-vig fair odds formula
For a simple two-outcome market, no-vig fair odds scale each implied probability by the total book percentage.
Implied probability A = 1 / decimal odds A
Implied probability B = 1 / decimal odds B
Book percentage = implied probability A + implied probability B
Fair probability A = implied probability A / book percentage
Fair probability B = implied probability B / book percentage
Fair odds = 1 / fair probability
Worked example
Suppose both outcomes are priced at decimal odds of 1.91. Each side has an implied probability of about 52.36%, so the book percentage is about 104.71%.
| Outcome | Decimal odds | Implied probability | No-vig fair probability | No-vig fair odds |
|---|---|---|---|---|
| A | 1.91 | 52.36% | 50.00% | 2.00 |
| B | 1.91 | 52.36% | 50.00% | 2.00 |
This example shows how the margin is removed in a simple two-outcome market. It does not prove that either side is a good bet.
No-vig odds and value betting
No-vig odds are not the same as value betting. They estimate fair probabilities from the market prices you enter. Value betting also depends on whether your own probability estimate is better than the available price.
Real markets can include commission, exchange liquidity, void rules, dead heat rules, each-way terms, deductions and other conditions. Those details can change the practical result.
When to use the calculator
Use the No-Vig Fair Odds Calculator when you want to understand the margin in a simple two-outcome market and estimate the fair probabilities after removing overround.