No-vig fair odds calculator
Both sides added together tell you what the market is charging you to be there.
Every two-way price contains a margin. Add the two implied probabilities: if they come to more than 100%, the excess is the house’s. Divide each side by the total and you get the price the market would show if it were only pricing the question, which is the number worth comparing your own estimate against.
100% means no vig at all—
Overround, vig, hold — the same thing three times
Take a two-way market priced −110 on both sides. Each side implies 52.38%. Together that is 104.76% — the overround. The hold, the fraction of every dollar traded the venue keeps if it balances the book, is 4.76/104.76 = 4.55%.
The no-vig fair price is each side divided by the total: 52.38/104.76 = 50%. That is the proportional method, which is the standard one and the one this page uses. It assumes the margin is spread evenly across both sides. On lopsided markets that assumption is known to be imperfect — favourite-longshot bias means the margin usually sits heavier on the long shot — so treat a no-vig price on a 5¢ contract as an estimate, not a measurement.
On Polymarket the arithmetic works but the story is different: the two sides are the two halves of the same token pair, so they sum close to 100¢ and there is no bookmaker margin in the price at all. What you actually pay sits in the spread and in the taker fee.
Questions
What does no-vig mean?
The price with the venue's margin removed — what the market implies about the question alone, before the cost of being allowed to trade it.
How do you calculate no-vig odds?
Convert both sides to implied probability, add them, then divide each side by that total. Two sides at 56% and 47% sum to 103%; the fair prices are 54.4% and 45.6%.
Do prediction markets have vig?
Not in the bookmaker sense. On Polymarket a binary market's two sides are one token pair and sum to about $1. The cost of trading shows up as the bid-ask spread and, for takers, a fee that depends on the category.