An Elo calculator turns two ratings into an expected result. A 1650 player against a 1520 player expects to score 67.9%, which the free calculator above also turns into fair odds of 1.47 if a draw can’t happen. Win, and you gain 6.4 points with a K-factor of 20. Lose, and you drop 13.6.
The same maths drives chess ratings, club football models and plenty of betting systems. It only needs the two numbers and a sense of how quickly ratings should move.
Elo calculator: the formula
Expected score for A = 1 ÷ (1 + 10^((B − A − home advantage) ÷ 400)) New rating = old rating + K × (actual score − expected score)
A win scores 1, a draw 0.5 and a loss 0. Every 400 points of difference is a factor of ten in the odds: a 400-point favourite expects about 91%, a 200-point favourite about 76%.
K decides how big each update is. FIDE uses 40 for new players, 20 for most and 10 for players who have reached 2400. Football models often use 20 to 30, plus a home advantage worth 50 to 100 points.
Turning Elo into betting odds
An expected score isn’t a win probability when draws are common. In football, 67.9% expected might be 55% win, 25% draw and 20% loss. Put a draw rate in and the calculator splits the expected score that way, then prices each result. Compare those fair odds with the bookie’s: if they offer more than your fair price on your rated side, that’s the value. Run it through the expected value calculator to see what it’s worth per bet.
Elo knows nothing about injuries, rotation or a red card in the 10th minute. Treat it as a base price. For goal-based football prices, the Poisson calculator works from expected goals instead, and the Kelly criterion calculator sizes a stake once you think you have an edge.
For cricket, the DLS calculator handles rain-affected targets and net run rate.
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