Your rating against theirs.
An even match: the rating system expects you to score about half the points on offer.
Your new rating after a win, a draw or a loss.
Enter your rating and your opponent's and the calculator shows how many points the rating system expects you to score, then your new rating after a win, a draw or a loss. Below that, set a target rating and how many games you play a week, and it works out how many games the climb takes at the rate you actually score. It is free and needs no account.
Elo turns a rating gap into an expected score. Your expected score against an opponent is 1 / (1 + 10^((their rating minus yours) / 400)). A 100-point gap gives the stronger player an expected score of 64%, 200 points gives 76%, and 400 points gives about 91%.
After the game, your new rating is your old rating plus K times the difference between what you scored and what you were expected to score. A win counts 1, a draw 0.5 and a loss 0. Beat a stronger opponent and you scored far more than expected, so you gain a lot. Lose to a weaker one and you lose a lot for the same reason.
K sets how far one game can move a rating. FIDE uses 40 for new players until they have 30 rated games, and for most juniors below 2300, then 20 for players below 2400, and 10 once a player has reached 2400. 32 is a common default elsewhere. A larger K reacts faster to new results, and a smaller one keeps an established rating steady.
The planner assumes you keep playing people at your own level, which is what matchmaking does on every chess site. Against your own level you are expected to score 50%, so each game gains you K times the amount you score above 50%. At 56% and K 32 that is about 1.9 points a game, and the calculator divides the gap to your target by it. Scoring exactly 50% keeps a rating where it is, which is what a rating means.
Chess.com and Lichess do not use Elo. Both use Glicko systems, which also track how certain your rating is, so a new or inactive account moves by more than Elo would suggest. For an established rating, Elo is a close guide to what a result is worth. For the games themselves, a Game Report shows where the points were won and lost.
Your expected score is 1 / (1 + 10^((opponent rating - your rating) / 400)). After the game your new rating is your old rating plus K times (your result minus that expected score), where a win counts 1, a draw 0.5 and a loss 0.
FIDE uses 40 for new players until they have 30 rated games, and for most juniors below 2300, then 20 below 2400 and 10 once a player has reached 2400. 32 is a common default elsewhere. A bigger K moves your rating further after each game.
No. Both use Glicko systems, which also track how certain your rating is, so their changes can differ from an Elo calculation, especially on new or inactive accounts. Elo gives a close guide for an established rating.
More than a loss costs. At K 32, a player rated 100 points lower gains about 20 for a win and loses about 12 for a loss, because the system only expected them to score 36%.
Yes, with no account needed.