Parlay odds calculator

The math for independent legs

Every leg has to win, so for legs whose results do not depend on each other the decimal odds multiply, and so do the chances. Two legs at -110 are 1.909 × 1.909 = 3.64 (+264); three are 6.96 (+596). With a chance for each leg instead of a price, choose Chance in %: the slip's chance is the product of the legs' chances, and its fair odds are the price that chance implies, as the SportsFathom slip prints them.

The book's margin compounds too. A -110 leg implies 52.4% where its no-vig chance is 50.0%; three of them together imply 14.4% where the no-vig chance is 12.5%, so the price falls further short of fair with every leg added.

Same-game legs are not independent

Legs from the same game move together. A team covering the spread and its quarterback going over his passing yards tend to land together; an over on the total and a low-scoring first half pull against each other. Multiplying such legs as if they were independent gives the wrong chance, which is why books price same-game parlays their own way. The SportsFathom slip prices the legs on one game together from the model's joint simulation of that game, and only multiplies across different games.