Why bookmakers' chances add up to more than 100%
Add up the chances behind both sides of a bet and you get more than 100%. The extra is the bookmaker's profit margin.
Over at 1.90 → 52.6% · Under at 1.90 → 52.6%
Total 105.3%, so the margin is 5.3%
Total 105.3%, so the margin is 5.3%
To compare fairly, scale both back so they add up to 100%. Here that gives 50% each. The fair-odds calculator does this for any price.
Show the maths
Fair chance of each outcome = (1 ÷ its price) ÷ S, where S is the sum of (1 ÷ price) across every outcome. This is called proportional margin removal.