About EloRatingSystem

EloRatingSystem is a free set of tools for the Elo rating system: a calculator, a league and leaderboard tool, a win probability calculator and a performance rating calculator, plus guides that explain how ratings work.

How we keep it accurate

• Rules from the source. FIDE presets follow the FIDE Rating Regulations (effective 1 March 2024, with the 400-point rule amended from 1 October 2025). US Chess presets follow the US Chess rating system specification dated 6 April 2026. The sources are listed on each page.
• Tested math. Our calculations are unit-tested against published examples: FIFA's SUM example (+17 points), the US Chess specification's N′ and K tables, FIDE's lookup tables and K rules, and Glickman's Glicko-2 worked example (1464.06 / 151.52 / 0.05999).
• No invented numbers. Facts link to rule books, papers or the organisation's own pages. Where something is our opinion, such as a suggested K for an office league, we say so.

Independence

We aren't affiliated with FIDE, US Chess, FIFA, Lichess, Chess.com, Microsoft or any other organisation mentioned. Names are used only to describe their published rating methods. The site may show advertising in the future. Ads won't change how any calculation works.

Found a mistake? See the contact page.