Fair Odds

Fair odds represent what a price would be in a perfectly efficient, margin-free market. Because they carry no vig, the two sides of a fair two-way market imply probabilities that sum to exactly 1. Fair odds are effectively the odds form of no-vig probabilities — convert the de-vigged probability of each side back into American or decimal odds and you have the fair line.

They are usually derived from a sharp, high-limit market by removing the vig: take each side’s raw implied probability, divide by the overround so the two sum to 100%, then convert back to odds. For a market at -110 / -110, the fair probabilities are 50% / 50%, which converts to fair odds of +100 / +100 (decimal 2.00 each). Fair odds therefore tell you the price at which a bet has zero expected value.

Fair odds are the benchmark for value betting. If a different book offers a price longer (more generous) than the fair odds — say +110 against a fair +100 — that gap is your edge and the bet carries positive EV. Comparing available prices against fair odds is the standard way to surface mispriced lines and quantify how much value a bet actually holds.