No-Vig Calculator

Frequently asked

What is a "no-vig" or "fair odds" calculation?

Every posted market has a built-in bookmaker margin (the "vig"), which is why implied probabilities across all sides of a market sum to more than 100%. Removing the vig means normalizing each side’s implied probability so the full set sums to exactly 100% — the odds you’d see in a theoretically zero-margin market.

How is the overround (vig) calculated?

Convert each side’s American odds to decimal, take the implied probability of each (1 / decimal), and sum them. In a normal market that sum — the overround — is greater than 100%; the amount over 100% is the vig.

How do you get each side’s fair probability from the overround?

Divide each side’s raw implied probability by the overround. That normalizes the whole set back to exactly 100% while preserving the relative weight between sides. Fair decimal odds are then 1 / fair probability, converted back to American for display.

What if the implied probabilities sum to under 100%?

That’s not invalid input — it just means the odds you entered were already more generous than "fair" (an arbitrage-shaped price). Normalizing up to exactly 100% in that case makes the fair odds worse (lower payout) than the input on every side, the opposite of the normal vig-stripping direction. This calculator handles it without erroring.

Does this calculator use live sportsbook odds?

No. It runs entirely in your browser on the numbers you type in — no live odds feed, no vendor data, nothing sent to a server. It’s a reference implementation of the no-vig math, not a betting page.