Amazon’s membership program, Amazon Prime, will likely be used by 50 percent of U.S. homes by the end of 2017, Cowen and Co. forecasted in its monthly survey of 2,500 U.S. consumers.

Amazon keeps its number of Prime subscribers private. But Cowen and Co. analyst John Blackledge estimated in a note to investors last week that there were more than 54 million U.S. Prime subscribers in July, up from the 46 million subscribers in July 2016.

The household penetration of Amazon Prime (courtesy of Cowen and Co.)

Blackledge called Amazon Prime the company’s “critical driver.” He cited the success of Amazon’s Prime Day—the annual 24-hour period that pushes special promotions and, this year, led to a record number of Prime sign-ups.

“Prime has maintained healthy growth despite its scale,” Blackledge said.

(Photo courtesy of Amazon)