Song placement is calculated using sales information from Nielsen SoundScan, the year-end charts are calculated by a very straightforward cumulative total of yearlong sales and airplay points. This gives a more accurate picture of any given year’s most popular tracks, as a song that hypothetically spent nine weeks at number one in March could possibly have earned fewer cumulative points than a song that spent six weeks at number three in January. Interestingly, songs at the peak of their popularity at the time of the November/December chart-year cutoff many times end up ranked lower than one would expect on a year-end tally, yet are ranked on the following year's chart as well, as their cumulative points are split between the two chart-years.