Fair Odds & No-Vig Probability Calculator
Understand the price. Check the numbers.
Free to use · No sign-in needed · Calculations stay in your browserFrom bookmaker prices to no-vig estimates
Remove the overround from a complete market to estimate each outcome’s probability and fair price. Compare proportional and power methods—no API or stake required.
Your market
Manual oddsIllustrative prices to start. Each tab keeps its own inputs. Replace every price with one complete market from the same bookmaker and time.
Decimal odds include your stake. Example: 2.50.
Include all mutually exclusive outcomes with matching settlement rules. This tool assumes one full winner and full losses on the rest—not pushes, half wins/losses or overlapping selections.
Your no-vig estimates
Updates instantly- Original overround
- 4.71%Implied total minus 100%
- Original implied total
- 104.71%Before any adjustment
Divides each implied probability by the market’s implied total. Relative probabilities stay the same.
| Selection | Entered odds | Implied % | No-vig % | Fair odds |
|---|---|---|---|---|
| Selection A | 1.91 | 52.36% | 50.00% | 2.0000Decimal |
| Selection B | 1.91 | 52.36% | 50.00% | 2.0000Decimal |
Calculations use full precision; displayed percentages may not add to exactly 100% after rounding. Fair odds use your selected odds format.
These are market-derived estimates, not true probabilities or a prediction model. Removing the margin does not prove a bet has value; different methods can give different answers.
How the margin is removed
Convert each price to decimal odds O. Its raw implied probability is q = 1 ÷ O. Add these to get S, the market’s implied total; overround = (S − 1) × 100%.
Proportional: p = q ÷ S. This scales all implied probabilities by the same factor. Fair decimal odds = 1 ÷ p.
Power: find one exponent k so that the sum of qᵏ across all outcomes equals 1. Each estimated probability is p = qᵏ. This allows a different margin allocation between favourites and longshots; it is not automatically more accurate for every market.
A 3-way example
At 2.00 / 3.50 / 4.00, the raw implied probabilities are 50.00% / 28.57% / 25.00%: a total of 103.57%. Proportional de-vigging gives approximately 48.28% / 27.59% / 24.14%, or fair decimal odds of 2.0714 / 3.6250 / 4.1429.
When not to use this calculation
A 3-way football market must include home, draw and away for the same period. For a multiway market, include every possible winner, including “Other” or “Field” when needed. Two opposing prices on a market with a push do not reveal unconditional win probabilities.
Asian quarter-lines, dead heats, exchange commission and other partial settlements need a different model. For constructing Asian lines, use the Asian Handicap Calculator & Builder; it does not turn quarter-line prices into unconditional win probabilities.
Method background: Clarke, Kovalchik & Ingram, “Adjusting bookmaker’s odds to allow for overround” (2017).
Calculation tools, not betting recommendations. Nothing is added to your ledger and no bets are placed. Currency changes the display only, not exchange rates. Gambling involves risk—only stake what you can afford to lose.