JPMorgan Chase & Co.‘s active mobile users totaled about 21 million last quarter, the bank announced today.

JPM is the first bank to report more than 20 million total active mobile users. JPM made the announcement as part of its second quarter earnings release.

The 20 million mark is a landmark in mobile banking. Chase has been growing its AMUs at a remarkable clip. Just two years ago, Chase had 14 million mobile users, which means its mobile banking user base has jumped 50% since then. The bank’s year-over-year mobile growth rate was 22%.

Wells Fargo & Co., by contrast, recorded “nearly” 16 million AMUs last quarter, the bank announced. While Marianne Lake, JPM’s CFO, said during the bank’s earnings conference call today that “We are the largest and fastest growing among major banks” in mobile accounts, Wells’s mobile banking growth rate is similar to Chase’s.

Online and mobile not only provide a “fantastic customer experience,” to users, but also a “lower cost to serve” for the bank, Lake said.

Mobile banking has become a centerpiece of JPM’s retail banking business.

Jamie Dimon, chairman and chief executive of JPMorgan Chase, said this morning that Chase was trimming its branch offices, in part because more customers are switching to mobile applications. He said Chase, which ended the quarter with 5,504 branches, closes branches in some locations and opens them in others based on city-by-city analysis.

“We’re not getting smaller because we’re guessing,” Dimon said. “We’re getting smaller because people are doing more in mobile.”

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