How do the rankings work? It’s a commonly asked question of the professional game, with even the most dedicated fans occasionally overwhelmed by the variables.

The key points to note are largely consistent on both the ATP and WTA Tours, with rankings based on a rolling 12-month period– so in any given week, a player’s ranking will be based on their performances in the previous 52 weeks.  In the simplest terms, the more points a player earns the higher their ranking will be.

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It’s the “best of” scenario for the highest ranked players that can make rankings confusing. A male player’s overall ranking can be based on their best 18 results while a woman’s overall ranking can be based on her best 16. The Grand Slams and certain higher level events carry the highest number of rankings points and must be counted in those “best of” equations (see table below).

On the ATP Tour, the nine mandatory events besides the Grand Slams are the nine Masters 1000 tournaments (Indian Wells, Miami, Monte Carlo, Madrid, Rome, Toronto, Cincinnati, Shanghai and Paris). Additionally, “commitment” players (those who were ranked in the top 30 at year-end 2013) can also count their best six events from lower level events.

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There are four Premier mandatory tournaments that must be counted on the WTA Tour (Indian Wells, Miami, Madrid and Beijing). For top 20 players, the best two results at Premier 5 events (Doha, Rome, Cincinnati, Montreal and Wuhan) will also count. As with the men, the remainder of “best” tournaments can comprise any of the lower level events.

Each week, the rankings points that a player earned at the same time in the previous year expire, which is why you’ll often hear players or commentators talking about “defending points”. If a player won a Grand Slam in the same week of the previous year but lost in the first round of the event in the current year, their ranking would drop.

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Injury or other circumstantial absences can therefore be  costly for the world’s top  players – if they’re not able to contest a Grand Slam or top-tier events, they receive zero rankings points.

Players can also gain rankings points at season-ending events (for which the top eight players in the men’s and women’s game qualify).