Free tool
No-Vig / Fair Odds Calculator
Enter the odds on both sides of a two-way market. This strips out the bookmaker's margin (the vig) proportionally, so you can compare prices across books on a level footing.
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How this is calculated
Each side's implied probabilityis 1 ÷ decimal odds. The two implied probabilities sum to slightly over 100%, and that excess is the vig. To remove it proportionally:
fair probability (A) = implied A ÷ (implied A + implied B)
This is the standard proportional method: simple and good enough for most comparisons. It isn't the only de-vigging method (Shin's method and others exist and can differ slightly on very skewed markets), but it's the one most bettors mean by "no-vig odds."
What this is useful for: comparing the same market across two bookmakers with different margins, or getting a cleaner probability baseline before estimating your own edge. See the Kelly & Value Calculatorfor the next step.
Worked example: 1.80 vs 2.10
- Implied probabilities: 1 ÷ 1.80 = 55.56 % and 1 ÷ 2.10 = 47.62 %.
- They add up to 103.17 %, so the bookmaker margin is 3.17 %.
- Fair probabilities: 55.56 ÷ 103.17 = 53.85 % and 47.62 ÷ 103.17 = 46.15 %.
- Fair odds: 1 ÷ 0.5385 = 1.857 and 1 ÷ 0.4615 = 2.167. These are the prices the market would show with no margin at all.
Common mistakes
- Comparing your own estimate with the raw implied probability (55.56 %) instead of the fair one (53.85 %). That alone can invent an edge of almost two points.
- De-vigging one side only. The margin is shared across both sides of the market, so you always need both prices.
- Mixing books: take both prices from the same bookmaker, otherwise the "margin" is meaningless.
In tennis
Tennis match-winner markets are two-way, so this method fits them well. Margins differ a lot between books and between main-tour and Challenger matches; we skip markets above 8 % margin entirely, because the fair price behind a very wide market is too uncertain.
Read next: Kelly & value calculator · How to calculate implied probability · Model vs. market for every match today
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