Betting maths and calculators
What's the best way to find the bookmaker margin in a two-outcome market?
Direct answer
For two mutually exclusive, exhaustive outcomes with decimal prices d₁ and d₂, the overround is (1/d₁ + 1/d₂ − 1) × 100%. For 1.90/1.90 it is approximately 5.26%.
How to use this answer
This answer is based on the mathematical principle or published rule identified in the source below. If the question involves a live betting market, confirm its settlement definition before applying it to a specific bet.
Add the implied probabilities of both offered prices and subtract 100%; the excess is the overround.
Use the precise stake, decimal odds, market terms and outcome probabilities when calculating the result. Expected value measures an average over hypothetical repetitions, not a guaranteed profit.