Bookmaker margin and overround explained
Calculate overround for 1X2 and two-way markets, compare equivalent prices and understand the limits of a margin estimate.
OddsCapo educational content · Illustrative prices, not current offers
Margin, vig and overround
Bookmaker margin is often described using the excess of quoted implied probabilities over 100%, known as overround. The word vig is also used for a pricing charge, although terminology differs between markets.
For a complete win-or-lose market, overround = (sum of 1 / odds − 1) × 100. All outcomes must come from the same bookmaker, rules and observation time. Missing an outcome invalidates the calculation.
Implied probability: convert decimal odds to percentagesExamples for two-way and 1X2 markets
Two opposing outcomes both priced at 1.90 imply 52.63% each. Together they imply 105.26%, giving about 5.26% overround. If both are 1.95, the overround is about 2.56%.
A 1X2 market at 2.00, 3.50 and 4.00 implies a total of about 103.57%, or 3.57% overround. These are theoretical examples, not current bookmaker offers. Refund-bearing lines need care because the simple win-or-lose formula does not capture push probabilities.
Lower margin is not always the best individual price
A bookmaker with a lower overall margin may still have a lower price on the specific selection you want. Compare the individual odds as well as the whole market. A small difference can change the payout without changing the match itself.
Do not compare a regulation-time hockey market with one including overtime, or a total of 2.5 with one of 3.0. Different settlement rules can matter more than a small apparent margin difference.
What the margin does not tell you
Overround is a feature of the quotes, not a guaranteed percentage of the stakes that a bookmaker earns. Realised profit also depends on which selections are backed, the results and operational factors. It does not reveal your personal expected loss on every possible bet.
Exchange commission, fees and promotional conditions need separate treatment. A low displayed margin is not proof that a bookmaker is suitable for you or that a bet has positive expected value.
Compare in a match
Choose a match and the same market, selection and line. Inspect the timestamps in its history and confirm the available price and rules at the bookmaker before betting.
Related concepts
Implied probability: convert decimal odds to percentagesValue betting: expected value without guaranteesClosing odds: the last pre-match price explainedSources and method
Definitions and settlement are supported by the educational material below. These sources are commercial operators; their marketing is not evidence of future profit. Worked calculations are our own.
18+. Gambling involves the risk of losing money. No guide, graph or calculation guarantees profit. Responsible gambling.