Apple Music appears to be growing on listeners.
The music subscription service has surpassed the 20 million subscriber milestone just 18 months after its launch, Billboard reported Tuesday. That number represents growth of 15 percent since the company announced in September it had accumulated 17 million paying customers since it launched in June 2015.
Impressive as that growth is, Apple Music's subscriber list is still half the size of Spotify. As of September, the rival music streaming service had 40 million paying subscribers worldwide, up from 30 million paying subscribers in March, according to market researcher Statista.
The growth of both services underscores the growing popularity in streaming music. The number of on-demand streams in the US nearly doubled last year, according to researcher Nielsen's year-end music report. Fans logged nearly 145 billion audio streams in 2015, up 79 percent from the previous year, the researcher found.
Apple did not immediately respond to a request for comment but told the Billboard that much of that success can be attributed to Apple Music's launch of several No. 1 albums.
"It's been quite a year," Eddy Cue, Apple's chief of internet software and products, told Billboard. "We were thrilled to see that we could take [artists'] passions and drive them all the way to No. 1. Chance the Rapper, who we put on Apple Music exclusively, hit the top 10 on the Billboard charts and I can't recall that being done before."