What it means
For a market with exclusive outcomes, convert each odd to 1/odds and add them. The amount above 100% is a simple approximation of the market margin.
Odds and data
Bookmaker margin (overround)
Odds usually include a margin: the implied probabilities of all options add to more than 100%.
Example
If two outcomes are 1.80 and 2.05, the raw probabilities are 55.6% and 48.8%, totaling 104.4%. The extra 4.4 percentage points are the simplified overround.
Watch out for
Margin is not the outcome of one wager. It explains why a market probability needs context.
Educational content, not betting advice. Odds do not remove risk; check the operator's rules and stop if gambling is no longer fun or controlled.
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