The number of user accounts on the Robinhood trading app has blown past E*Trade, hitting 4 million. That’s double where it was a year ago.

Robinhood, beyond its mobile-first focus, lets traders speculate in both stocks and cryptocurrencies without commissions. That has greatly increased its popularity with traders, especially millennials.

E*Trade, which has long been the preferred tool of individual stock traders, reported 3.7 million accounts at the end of March.

Robinhood officials say they expect the growth to continue as they roll out additional features in the months and years to come.

“Crypto has certainly added to our growth,” Baiju Bhatt, Robinhood co-founder and co-CEO told CNBC. “In the next couple of years I think you’ll see Robinhood looking like a full-service consumer finance company.”

Robinhood Crypto launched in February and is currently available in 10 U.S. states. The company is rapidly expanding the service to new states, securing the necessary licenses for each as fast as it can. Bhatt tells Fortune he expects the offering to roll out country-wide by the end of 2018.

The addition of crypto trading has boosted Robinhood’s valuation to $5.6 billion. The company recently raised $363 million in a Series-D investment round. It is now the second most valuable private fintech startup in the U.S. after Stripe, the online payments company.