Win Probability Calculator
Turns ratings or records into a chance of winning.
Side A wins a game
— %
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
Side A wins the series — %
Side B wins a game — %
Reading this —
The formula
Elo: P = 1 ÷ (1 + 10^((Rb − Ra) ÷ 400)) Win rates: P = a(1 − b) ÷ (a(1 − b) + b(1 − a))
The win-rate version is Bill James’s log5 method. The series figure adds up every way of reaching the winning number of games.
What to watch out for
Only the two fields for the chosen method are used. A long series favours the stronger side more than a single game does.
Frequently Asked Questions
What does a 100-point Elo edge mean?
About 64.0% per game, or 78.3% over a best of 7.
What if a 60% team plays a 50% team?
Log5 gives the 60% team 60.0%.