What is overround?
Overround is the amount by which the implied probabilities of all outcomes in one betting market add up to more than 100%. It is the bookmaker's margin expressed as a percentage: prices of 1.90 and 1.90 imply 105.26% in total, so the overround is 5.26%.
Definition
Every price corresponds to a probability: 1 divided by the decimal odds. If a market were priced with no charge, those probabilities would total 100%, because exactly one outcome must happen. In a bookmaker's market they total more. The surplus is the overround.
Illustrative example
A tennis match has two outcomes, priced 1.60 and 2.30. The implied probabilities are 62.50% and 43.48%, which total 105.98%. The overround is 5.98%, and the prices return 1 ÷ 1.0598 = 94.36% of stakes on average.
Why the word matters
The overround is the cost of betting written into the odds. It is not shown as a fee, so the only way to see it is to add the market up, by hand or with the margin calculator. A larger overround means a larger average cost; it says nothing about which outcome will occur.
The inputs must be on display before a bet is accepted: regulation 23(1) of the Gambling Control (Conduct of Gambling Operations) Regulations, 2026 requires a licensee to clearly display betting odds, rules and terms applicable to each bet.
Related terms
Margin, vig and juice are used for the same idea. Payback (or payout rate) is its counterpart: 1 divided by the total implied probability. The full method, including how to strip the overround out of a set of prices, is in the guide on calculating the bookmaker's margin.
Questions and answers
Is overround the same as margin?
In everyday use, yes. Both describe the excess of total implied probability over 100%. Some writers use margin for the share of stakes kept on average, which is 1 minus 1 divided by the total; the two figures are close but not identical.
What does an overround of 0% mean?
It means the implied probabilities add up to exactly 100%, so the prices carry no margin. Such prices are called fair odds and are a reference point for calculation, not something a bookmaker's market normally shows.