Fair odds: how to tell if a bet is good value

Every probability has a fair price. Fair decimal odds are simply 1 divided by the probability: a 50% chance is fair at 2.00, a 25% chance at 4.00, and an 80% chance at 1.25.

Why it matters

Bookmakers build a margin into their odds, so their prices are almost always shorter than fair. If you only ever bet at shorter-than-fair odds, you lose money in the long run even if your picks are good. Value appears when a bookmaker’s odds are longer than the fair price for the true probability.

A worked example

Our model gives a home win a 60% chance, so fair odds are 1.67. One bookmaker offers 1.80, which is longer than fair, so the model sees value. Another offers 1.55, which is shorter, so the bookmaker is taking an extra cut.

The catch

Value is only as good as the probability behind it. Our market pages show fair odds next to every pick, and the track record shows whether the model’s probabilities hold up.