Implied probability calculator

How it works

Each decimal price converts to probability as 1 ÷ odds. If the bookmaker took nothing, the probabilities of every outcome would add up to exactly 100%. They always add up to a little more: that excess is the overround, also called the vig or juice.

The payout is 1 ÷ total: the share of stakes the book returns on average if its prices are accurate.

Fair odds come from removing the margin proportionally, dividing each probability by the total. It is the simplest method; others (Shin, power) put more of the margin on the less likely outcome.

It is useful for comparing books: on the same game, the one with the lower margin offers better prices overall. A price that beats another book’s fair odds is a sign of value.

Formulas

• Implied probability = 1 ÷ decimal odds
• Total = p₁ + p₂ (+ p₃)
• Margin (overround) = total − 1
• Payout = 1 ÷ total
• Fair probability = pᵢ ÷ total
• Fair odds = odds × total

Worked example

A standard line at -110 / -110: each side has an implied probability of 52.38%, 52.38%. Together they make 104.76%, so the vig is 4.76% and the payout 95.45%. With the vig removed, the fair price on each side is +100, +100.