How ranking points work
A rolling 52-week total, and why that single rule explains most of what happens to the rankings.
Grand Slam points
A major is worth 2000 ranking points to the winner, more than any other tournament and roughly twice what a 1000-level title pays. There are only four of them in a year, which is why a single good fortnight here can move a player further up the list than a strong month anywhere else, and why the points are so painful to defend twelve months later.
The other side of that arithmetic is what happens to a defending champion. Those 2000 points sit on their total for exactly one year and then vanish on the Monday after the tournament ends, whether or not they play well. A champion who reaches the quarter-finals the following season loses ground in the rankings while winning four matches.
The 1000-level events
A 1000-level title is worth 1000 ranking points, half of a major and the second-largest prize in the sport. There are nine of these on the men's calendar and ten on the women's, so they carry far more of the ranking than the four majors do: it is perfectly possible to build a top-ten season without a deep run at a Grand Slam, and much harder to do it without points from this level.
They also work as the qualification race for the season finals. By the autumn the players chasing the last two places in the eight are usually separated by the result of one 1000-level event, which is why entry lists at this level are so complete.
The season finals
The season finals pay points differently from everything else on the calendar, because there is no draw to progress through. Points accumulate match by match through the group stage and then for the semi-final and the final, so an undefeated champion collects considerably more than one who stumbled in a group and recovered.
Qualification itself is the harder part. Only eight singles players get in, decided by points earned across the whole season, and the race is usually still open when the Asian swing ends. That is why autumn tournaments matter more to the players ranked between eight and fifteen than their prize money suggests.
Why a player drops without playing badly
This is the part that confuses people watching the list move on a Monday. Points are not a season total that resets in January. Every result sits on a player's total for exactly 52 weeks and then falls off on the anniversary of the tournament, whether or not they entered it this year.
So a champion defending a title is not merely trying to win again: they are trying to replace points that are leaving regardless. Reaching the quarter-finals of a tournament you won last year is a good week and a bad one at the same time.
Current lists: ATP top 50 and WTA top 50.