YES pricevsNO price
Implied Probability Calculator
Enter a single price or odds quote to see the probability it implies, or enter both sides of a market to see the vig and the vig-free probability on each side.
From a single price or odds
Implied probability
58.00%
Two-sided market: find the vig
Enter both sides' prices from the same market to see how much they overshoot 100% (the vig, or overround), and the vig-free probability on each side.
Overround (the vig)
5.00%
the market's built-in edge
Vig-free YES
52.38%
Vig-free NO
47.62%
| YES | NO | |
|---|---|---|
| Quoted price | 55¢ | 50¢ |
| Raw implied probability | 55.00% | 50.00% |
| Vig-free probability | 52.38% | 47.62% |
How this is calculated
From a single quote: a contract priced at P cents implies a probability of P%, full stop -- that's what makes prediction-market pricing simpler than betting odds. American, decimal, and fractional odds all reduce to the same number through their standard formulas (1/decimal odds is the probability; American and fractional are just different notations for the same decimal price).
From two sides: add YES's implied probability to NO's. If they sum to more than 100%, the excess is the overround -- on the default {55¢ YES, 50¢ NO} example that's 5.00%. To get back to a fair 100%, this page divides each side's raw probability by that sum: YES becomes 52.38% and NO becomes 47.62%.
This isn't a prediction. Removing the vig tells you what the two sides of the market think RELATIVE to each other, not what will actually happen. A vig-free 50/50 split still means the market is genuinely uncertain -- it doesn't mean either outcome is more likely than the price says.
Frequently Asked Questions
What does 'implied probability' actually mean here?
It's the probability a price or odds quote is claiming, read backward. A prediction-market contract priced at 55¢ pays $1 if it happens, so if the market is priced fairly, it must think that's 55% likely -- otherwise buying or selling the contract would be free money. The same logic runs through betting odds in any format: shorter odds always mean a higher implied probability.
Why do the two prices on a real market almost never sum to exactly 100%?
Because the market maker (or the exchange's own fee structure) builds in a margin, called the vig or overround. On the default numbers here -- YES at 55¢, NO at 50¢ -- the two prices sum to 105¢, an overround of 5.00%. That extra 5.00% isn't a real probability edge; it's the market's cut, and it's why you shouldn't read a 55¢ YES price as literally "55% and nothing else."
How does removing the vig actually work?
This calculator uses the proportional method: divide each side's raw implied probability by the sum of both. On the default example, YES's raw 55.00% and NO's raw 50.00% sum to 105.00%; dividing each by that sum gives a vig-free YES of 52.38% and NO of 47.62% -- which do add back to exactly 100%. This is sometimes called the "multiplicative" method elsewhere, because you're scaling (multiplying) each side by the same constant -- it's the identical calculation under two different names, not two different answers.
Is there a different way to remove the vig?
Yes -- the 'additive' (or Shin) method instead subtracts an equal share of the overround from each side rather than scaling both proportionally. For a two-way market the two methods usually land close together but not identical, and proportional scaling is the more common default because it treats both sides symmetrically regardless of how lopsided the market is. This calculator uses proportional throughout.
Can the two prices sum to less than 100%?
Yes -- that's an underround, and it means there's more available than the vig taking a cut; it can mean a genuine mispricing between the two sides (or two venues), which is exactly what the arbitrage calculator checks for. It's rarer than an overround because market makers set prices to protect their own margin, not give it away.
SidebySideCalc's prediction-market calculators apply standard odds, probability, and bankroll-sizing math to the numbers you enter -- they are not trading advice. Prediction markets carry real risk of loss and may be restricted or unavailable in some jurisdictions; nothing here names or endorses a specific trading venue.