Decimal odds are what €1 staked returns, stake included. Their inverse, 1 / odds, is the implied probability of the outcome. On a match, the implied probabilities of both players add up to more than 100%: the excess is the bookmaker's margin. Guide published on 05/09/2026.
This probability is called implied because it contains the margin: it is slightly higher than what the bookmaker really believes.
A match at 1.50 against 2.60. Implied probabilities: 1 / 1.50 = 66.7% and 1 / 2.60 = 38.5%. Total: 105.1%. The margin is 5.1%: of €100 staked on each side in market proportions, the bookmaker keeps about 5 whatever happens.
To recover the probabilities the market really believes, divide each implied probability by the total: 66.7 / 105.1 = 63.4% and 38.5 / 105.1 = 36.6%. That is the simplest normalisation; other methods put more of the margin on the underdog, whose odds are usually the most inflated.
On our corpus, the average market margin at opening is 6.15% on 220,859 settled singles matches since 2021, and 4.71% at the close. The average odds of the favourite are 1.43.
The opening odds are those first displayed, often several days before the match, set by a trader with little information. The closing odds are the last before the first serve: they have absorbed the bets, the news (withdrawal, injury, line-up) and the adjustments. They are the best public estimate of a match's probability.
Hence the most robust criterion for judging a bet after the fact: did it beat the close? Staking at 1.80 on a player who closes at 1.65 means you got odds above the final consensus, whatever the result. Over hundreds of bets, beating the close regularly is the sign of an estimate better than the market's. Our dataset gives both odds for every match. Download the data.
Three reasons, none of them a preference. Its margin is among the lowest on the market, so its odds are the closest to the probability. Its limits are high and it accepts winning accounts, so its odds reflect informed bettors' money instead of excluding them. And its closing odds are, by construction, the hardest to beat: the benchmark serious models measure themselves against. They are the odds our engines compare with their probability.
Implied probability = 1 / odds. Odds of 2.00 mean 50%, odds of 1.50 mean 66.7%, odds of 4.00 mean 25%.
The closing odds, just before the match, include all available information (withdrawals, form, bettors' money). Beating the close is the best indicator that a bet had value.
One of the lowest margins on the market, high limits and winning accounts accepted: its closing odds are considered the best public estimate of a match's probability.
See also: what is a value bet, the full methodology.