<P> Since the introduction rankings the method used to calculate a player's ranking points has changed several times . As of 2011, the rankings are calculated by totaling the points a player wins in his best eighteen tournaments, subject to certain restrictions . For top players the counting tournaments are the four Grand Slam tournaments, the nine mandatory ATP World Tour Masters 1000 tournaments, the player's best four eligible ATP World Tour 500 series tournaments and his best two results from ATP World Tour 250 series . Lower - ranked players who are not eligible for some or all of the top tournaments may include additional ATP 500 and ATP 250 events, and also ATP Challenger Series, and Futures Series tournaments . Players who qualify for the year - end ATP Finals also include any points gained at that tournament in their total, increasing the number of tournaments they may count to 19 . </P> <P> Roger Federer holds the records for both the most total weeks at No. 1 (310) and most consecutive weeks at No. 1 (237). Pete Sampras holds the record for the most year - end No. 1 rankings (six, all consecutive). Patrick Rafter spent the least time at No. 1 (one week). </P> <P> Lleyton Hewitt is both the youngest world No. 1 (20 years, 268 days) and youngest year - end No. 1, while Rafael Nadal is the oldest year - end No. 1 (31 years, 211 days). Roger Federer is the oldest No. 1 (36 years, 314 days). </P> <P> Roger Federer is the player with the longest time span between first and most recent dates at world No. 1 in the history of the ATP . He most recently held the top ranking the week of June 18, 2018, more than fourteen years after first becoming No. 1 on February 2, 2004 . </P>

Who become the oldest atp world number one