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The Billboard Hot 100 is the music industry standard record chart in the United States for songs, published weekly by Billboard magazine. Chart rankings are based on sales (physical and digital), radio play, and online streaming in the United States.
The weekly tracking period for sales was initially Monday to Sunday when Nielsen started tracking sales in 1991, but was changed to Friday to Thursday in July 2015. This tracking period also applies to compiling online streaming data. Radio airplay, which, unlike sales figures and streaming, is readily available on a real-time basis, is also tracked on a Friday to Thursday cycle effective with the chart dated July 17, 2021 (previously Monday to Sunday and before July 2015, Wednesday to Tuesday). A new chart is compiled and officially released to the public by Billboard on Tuesdays but post-dated to the following Saturday.
The first number one song of the Billboard Hot 100 was "Poor Little Fool" by Ricky Nelson, on August 4, 1958. As of the issue for the week ending on August 7, 2021, the Billboard Hot 100 has had 1,126 different number one entries. The chart's current number-one song is "Butter" by BTS.