The K-factor is the maximum number of rating points that can change hands in one game. A bigger K means a more volatile rating.

The FIDE values

  • K = 40 for a player's first 30 rated games, and for juniors under 18 whose rating is below 2300.
  • K = 20 for players who stay below 2400.
  • K = 10 once a player has reached 2400 at any time.

A worked example

You are rated 1600 and beat a 1800 player. Expected score: 1 / (1 + 10^(200/400)) = 0.24. You scored 1, so the change is K x (1 - 0.24).

  • With K = 40: +30 points.
  • With K = 20: +15 points.
  • With K = 10: +8 points.

Why it matters

New players climb quickly because the system is still learning their strength. Established players move slowly, which keeps ratings stable. If you play a nine round event you can multiply a typical change by the number of games to plan a realistic target.

Other systems

USCF and online platforms use different formulas. Lichess and Chess.com use Glicko-style systems that also track rating uncertainty, so you will see bigger moves after a break. The calculation here is the FIDE one.

Try your own numbers in the free Elo calculator, including the planner that tells you what score you need to reach a rating target.