Fair odds calculator

Bookmaker margin (also called overround, juice, or vigorish) is the profit margin built into every set of odds. If you add up the implied probabilities of all outcomes, the total will exceed 100% — that excess is the margin. For example, a coin flip should be priced at 2.00 for each side (50% + 50% = 100%), but a bookmaker might price it at 1.90/1.90 (52.6% + 52.6% = 105.2%), giving them a 5.2% margin.

The proportional method (default) removes margin proportionally to each outcome's implied probability. This means outcomes with higher probability absorb more of the margin, which reflects how most bookmakers actually apply margin.

The equal margin method distributes the total margin equally across all outcomes. This approach assumes the bookmaker applies the same margin percentage to every outcome.

Knowing the true fair odds is essential for identifying value bets. If the fair probability of an outcome is 50% but a bookmaker offers odds implying 45%, you have a +EV bet. This is the foundation of profitable betting — consistently finding odds that are higher than the true fair odds.