How ATP and WTA rankings work
The 52-week rolling system explained: mandatory events, points defence, qualifying cut-offs and what really moves the rankings.
The 52-week rolling system
Both the ATP and WTA rankings are not season-by-season. They are a rolling 52-week window: every Monday a new ranking is published using the points each player has scored over the previous 52 weeks. Last year's Australian Open is replaced this week by this year's Australian Open, that is why January and the European clay swing are points-defence minefields.
Mandatory and best-of counting events
For the men, the ATP counts 19 results: the four Grand Slams, the eight Masters 1000s, plus the seven best other results from ATP 500s and 250s. The Tour Finals add a further set on top. For the women, the WTA counts 16 results, the Slams, the four WTA 1000 mandatory events, the best two of the partial 1000s, and the best six of everything else, plus the WTA Finals.
Points defence
A player who won a tournament a year ago will lose every point from that title the day the new edition begins, replaced by whatever they earn this year. Defending a Grand Slam title means defending 2,000 points; failing to reach the second week typically means a heavy ranking drop.
Why the World No. 1 changes
World No. 1 changes hands when the chasing player's points-gained at an event exceeds the leader's points-defended. That is why a Masters 1000 final in March can flip the rankings even though the leader did not lose.