Historical rule
Base Elo (v1)
Uses K = 50, an expectation divisor of 600, and performance and title-context multipliers. Every fighter normally starts at 1500.
Current methodology
True Contender preserves the rule used for each bout. New versions apply from their effective date and do not generally rewrite earlier history.
Historical rule
Uses K = 50, an expectation divisor of 600, and performance and title-context multipliers. Every fighter normally starts at 1500.
Effective July 28, 2026
Adds effective-rating adjustments for inactivity and division changes. These adjustments change fight expectation but do not directly subtract from stored real Elo.
Effective September 5, 2026
Retains v2 and adds a symmetric, zero-sum bonus when the lower-rated fighter wins from a real pre-fight gap of at least 150 Elo points.
Every processed result stores its rule version, pre-fight ratings, expectation, multipliers, adjustments and post-fight rating so the calculation can be audited.