No-vig fair odds calculator
Enter the price of every outcome in a market, in cents or American odds, to remove the vig and see the fair probability of each one. Works for two-way YES/NO markets and for multi-outcome markets like elections.
How the calculation works
First turn every price into an implied probability and add them up. Anything above 100% is the overround:
overround = Σ implied − 1 hold = 1 − 1 / Σ impliedThe multiplicative method then scales each outcome so they sum to 100%:
fair_i = implied_i / Σ impliedThe additive method subtracts an equal share of the overround from each outcome instead. On Kalshi and Polymarket, use the ask price you would actually pay for each outcome; using the mid price gives an overround near zero.
Example
YES asks 55¢ and NO asks 48¢. The total is 103%, so the overround is 3% and the hold is 2.91%. Multiplicative fair prices are 53.4% YES and 46.6% NO.
Frequently asked questions
- What is the vig?
- The vig (vigorish, juice or overround) is the amount by which the prices of all outcomes add up to more than 100%. On a prediction market it mostly comes from the bid-ask spread: buying YES at 55¢ and NO at 48¢ costs $1.03 for a guaranteed $1.
- What is a no-vig or fair price?
- It is the probability each outcome would have if the overround were removed so the outcomes add up to exactly 100%. It is a better estimate of the market’s true view than the raw asking price.
- Multiplicative or additive: which method should I use?
- Multiplicative divides each price by the total, so favourites and longshots shrink in proportion. Additive takes the same amount off each outcome, which assumes the spread is flat. Multiplicative is the common default; the gap between the two grows with longshots.
- What does it mean if the total is under 100%?
- The outcomes are cheaper together than the $1 they pay. That usually happens when you combine the best price for each outcome across venues, and it is an arbitrage before fees.
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Calculations run in your browser and are estimates for education only, not financial advice. Venue fee schedules change; check the venue before you trade.