Win Probability Calculator

Calculate Elo-based win probability and post-match rating updates for head-to-head competition.

Player/Team A Rating

Player/Team B Rating

K-Factor

Actual Result (A)

Home Advantage (Elo pts)

Tab to move between fields

Win Probability A

50%

Win Probability B50%

New Rating A1,516

New Rating B1,484

Rating Change A16

Rating Difference0

Implied Decimal Odds (A)2

Rating Change B-16

How to Use This Calculator

Enter the current Elo rating for Player/Team A and Player/Team B.
Set the K-Factor (32 for general use; chess uses 10-40, NBA/NFL ~20).
Select the Actual Result for Player A (Win, Draw, or Loss).
Optionally add Home Advantage in Elo points (NFL ~48, NBA ~100).
Review Win Probability, updated ratings after the match, and implied decimal odds.

How the result changes with Player/Team A Rating

Player/Team A Rating: Current Elo rating of player or team A.
Player/Team B Rating: Current Elo rating of player or team B.
K-Factor: K-factor determines rating volatility. Chess uses 10-40; NBA ~20; NFL ~20.
Actual Result (A): Match result for player/team A.
Home Advantage (Elo pts): Home-court/field advantage in Elo points. NFL ~48, NBA ~100, soccer ~65.

Win Probability A: Pre-match win probability for player/team A.
Win Probability B: Pre-match win probability for player/team B.
New Rating A: Player A's updated Elo rating after the match.
New Rating B: Player B's updated Elo rating after the match.
Rating Change A: How many Elo points A gained or lost.
Rating Difference: A's rating minus B's rating (before the match).
Implied Decimal Odds (A): Fair decimal odds for A winning, implied by win probability.

Identify Input Parameters
4 parameters
Player/Team A Rating = 1500, Player/Team B Rating = 1500, K-Factor = 32, Actual Result (A) = 1 = 5 input(s) provided
Calculate Win Probability A
Win Probability A = expectedA * 100
50 = 50
Calculate Win Probability B
Win Probability B = expectedB * 100
50 = 50
Calculate New Rating A
New Rating A = ratingA + kFactor * (actualResult - expectedA)
1516 = 1516