Robinhood, the mobile brokerage app geared toward millennials, is closing in on E*Trade (ETFC) when it comes to the number of accounts in just under two years time.

In a blog post announcing the launch of a Web-based trading platform that includes research and discovery tools for investors, Robinhood said it crossed the three million user mark and has more than $100 billion in transaction volume. All told, the company said it has saved customers $1 billion in trading fees in the time frame. Up until the announcement of the Web-based platform, customers to Robinhood, who are mainly millennials, was resigned to making stock trades on their mobile phones. All trades on the platform are commission free.

Hitting more than 3 million users isn't only a milestone for Robinhood, but shines a light on E*Trade, which has been at the online brokerage game since 1982. As of the end of last year, the company had roughly 3.6 million brokerage accounts. In under two years, Robinhood has been able to bring on nearly as many customers as E*Trade has in 35 years.  When it comes to assets under management, Robinhood pales in comparison to E*Trade. The New York online broker ended the quarter with total customer assets of $365.3 billion, higher than the $307 billion it had at the end of last year’s third quarter. For its most recent quarter, the company reported EPS of  $0.49 a share, lower than the Wall Street expectations, which stood at $0.51 a share and 3% under what it did in the year-ago third quarter. Revenue of $599 million was able to surpass Wall Street, which expected it to come in at $598 million.

While E*Trade is a low-cost provider, Robinhood, thanks in part to a lot of venture capital funding, is able to lure millennials for one obvious reason: trading is free. Users who want access to margins and after-hours trading pay a $10 a month fee for Robinhood Gold, which helps cover the cost of commission-free trades. With more investors keenly aware of the amount they pay to trade stocks and with low-cost ETFs booming, it's not too surprising that Robinhood is growing at such a fast rate. In April the startup hit 2 million in customers and six months later it's up more than another 1 million. E*Trade, on the other hand, opened 26,000 net new brokerage accounts for the three month period ended in September.