How Parlay Probability Works

A parlay bet combines multiple individual bets (legs) into one wager, requiring all legs to win for the parlay to pay out. The true probability of a parlay hitting is calculated by multiplying the individual probabilities of each leg. For example, if you parlay two bets each with 50% win probability, the combined probability is 0.50 × 0.50 = 0.25 or 25%. As you add more legs, the probability decreases exponentially, making parlays increasingly difficult to win.

Understanding true parlay probability is crucial because sportsbooks often offer parlay payouts that don't reflect the fair odds. Each leg typically includes vig, and that vig compounds across the parlay. For instance, a 3-leg parlay with each leg at -110 (52.38% implied probability) has a combined implied probability of only 14.37%, yet the fair probability (assuming each leg has 50% true chance) should be 12.5%. This difference represents the compounded vig the sportsbook is charging.

This calculator computes the true combined probability of your parlay by multiplying the implied probabilities of each leg. It also shows you the fair odds the parlay should pay based on that probability. Add as many legs as you want, enter the odds for each leg (American or decimal), and see the actual win probability. Use this to evaluate whether a parlay offers value or if you're paying too much compounded vig.

Parlay True Probability Calculator

Compute the combined probability and fair odds for a parlay by multiplying the individual leg probabilities. Add as many legs as you like, then calculate to see the true probability of all legs hitting together. Select the odds format and enter each leg's price. Learn how parlay probability works