Fair odds calculator

Bookmaker margin (also called overround, juice or vigorish) is the profit built into every set of odds. Add up the implied probabilities of all outcomes and the total will exceed 100% — that excess is the margin. A coin flip should be priced 2.00 / 2.00 (50% + 50% = 100%), but a bookmaker prices it 1.90 / 1.90 (52.6% + 52.6% = 105.3%), a 5.3% margin. Typical margins run from about 2% at sharp books on major markets to 8–12% at soft books on niche ones.

Proportional divides each implied probability by the total, so every outcome gives up the same share of its price. It is the standard quick method and exact for two-way markets with symmetric margin.

Power raises each implied probability to the same exponent k, chosen so the total is exactly 100%. Longshots lose proportionally more of their implied probability than favourites, which matches the favourite–longshot bias that books build into their prices. It is the better choice for 3-way and multi-outcome markets.

Equal subtracts the same absolute amount from each outcome. It over-corrects longshots and is included mainly so you can see how much the method matters.

Fair odds from a sharp market are the benchmark for value betting. If the fair probability of an outcome is 50% and a softer bookmaker offers odds implying 45% (2.22), you have a +EV bet. Use the comparison column above to check any price against the fair line, then track whether the market moves your way with closing line value.