ELO Calculator

Yes. The chess.lc ELO calculator is 100% free, runs entirely in your browser, and requires no install, no signup, no account, and no credit card. There are no daily limits — calculate as many ratings as you want.

ELO uses two numbers: your expected score against an opponent (a probability between 0 and 1 based on the rating gap) and your actual score (1 for a win, 0.5 for a draw, 0 for a loss). The difference, multiplied by a K-factor, becomes your rating change. Beating a higher-rated player gains more points than beating a lower-rated one; losing to a lower-rated player costs more than losing to a higher-rated one.

FIDE uses K=40 for players with fewer than 30 rated games or rated under 2300, K=20 for the rest, and K=10 for players rated 2400 and above. Chess.com and Lichess use higher K-factors (around 32–40) so ratings move faster. If you're unsure, K=20 is the standard adult-rated default and matches most FIDE ratings.

Expected score E = 1 / (1 + 10^((R_opponent − R_you) / 400)). New rating R_new = R_old + K × (S − E), where S is your actual score (1 win, 0.5 draw, 0 loss). The 400-point divisor means a 400-rating gap gives the higher-rated player a 10× chance of scoring better. Arpad Elo published this formula in 1960 — it's still the same math FIDE uses today.

Because you were expected to win. If your expected score is 0.95 and you actually score 1.0, the gain is only K × (1.0 − 0.95) = K × 0.05 — roughly 1 point with K=20. Beating a higher-rated player gives a much larger expected gap (say 0.30) and therefore a much bigger swing. This asymmetry is by design — it stops sandbagging and rewards genuine upsets.

The expected-score formula is the same on every site, but Chess.com and Lichess both use the Glicko-2 system on top of it. Glicko-2 adds a rating deviation (uncertainty) that shrinks as you play more games, so your early swings are larger than pure ELO would predict. For long-time-control FIDE-style estimates, the standard ELO formula in this calculator matches the published FIDE math exactly.

Yes — set K=20 (FIDE standard) or K=24 (USCF average) and run a few of your recent rated games against opponents whose FIDE/USCF rating you know. The total change is a reasonable estimate. For an official rating you still need to play in a FIDE/USCF-rated event, but the math is identical to what the federations use.

For free Stockfish analysis with no daily cap, paste your PGN into chess.rodeo — it's free, no account required, and runs the same engine that powers paid game-review features. Combine the ELO calculator with a real engine review to understand both what you scored and why.