What makes a song a hit? In the “Gangnam Style” age the answer often has as much to do with its popularity on YouTube as any other factor.

This week the Billboard Hot 100, the magazine’s 55-year-old singles chart, takes a evolutionary step by incorporating YouTube plays into its formula. The move comes just in time for Baauer’s song “Harlem Shake,” the latest viral video phenomenon, which will make its debut at No. 1 this week thanks to the change.

“Harlem Shake,” a bass-heavy hip-hop track with no lyrics beyond a few samples, got little mainstream attention when it was released in May as a free download. But this month its popularity exploded on YouTube, as thousands of fans uploaded videos of themselves dancing — some might say simply flailing — along to the song. By last week more than 4,000 videos were going up each day.

Download sales and Spotify streams of the track also skyrocketed. But the remarkable trajectory of “Harlem Shake” led Billboard to move forward right away on its methodology update, something it had been in discussions with YouTube about for nearly two years, Bill Werde, the magazine’s editorial director, said on Wednesday.