If there's one trend to watch in the bank industry nowadays, it's the adoption of mobile banking. And if there's one bank that leads the way in this regard, it's JPMorgan Chase (JPM 2.51%).

The New York-based bank has more active users of its mobile banking app than any other bank. It reported 28.4 million active users at the end of the second quarter. And when you add customers that access their accounts from a personal computer as well, the total comes to 45.9 million active digital customers.

A bar graph shows JPMorgan Chase's growth in mobile banking users since 2012.

Data source: JPMorgan Chase. Chart by author.

One reason JPMorgan Chase has so many active mobile customers, defined as people who have logged into their accounts at least once within the past 90 days, is that it's the biggest bank in the United States, with $2.6 trillion worth of assets on its balance sheet. The runner-up is Bank of America (BAC 3.35%), which has a $2.3 trillion balance sheet.

But this alone doesn't explain JPMorgan Chase's success when it comes to persuading customers to use its mobile banking app. Consider this: While JPMorgan Chase is 14% larger than Bank of America when measured by assets, it has 24% more mobile banking users.

So, what explains the difference? One could argue that it's the mix of customers, as a higher share of individual customers relative to businesses could explain why so many more people use its mobile banking service.

And to a certain extent, there could be truth to this, as JPMorgan Chase's consumer and community banking division reports $648 billion in deposits compared with Bank of America's consumer bank, which has $644 billion in deposits.

An exterior view, looking up, of the JPMorgan Chase building.

Image source: Getty Images.

But even here, while JPMorgan Chase is indeed in the lead in this regard, it's neck and neck with Bank of America for all intents and purposes. This isn't to say customer mix isn't the explanation, only that you'd need to have access to more proprietary data to determine if that is indeed the case.

Another explanation has to do instead with the quality of JPMorgan Chase's mobile app. I'm a big fan of Bank of America's mobile app and use it all the time, but it's come in behind JPMorgan Chase the past two years in MagnifyMoney's annual survey of the best mobile-banking apps.

Both last year and this year, JPMorgan Chase earned the highest rating among big banks, narrowly outpacing Capital One Financial (COF 0.90%). Both JPMorgan Chase and Capital One were given ratings of 4.5. Bank of America earned a rating of 3.9. And the average among all banks included in the survey was 3.7.

As an aside, it's worth noting that Capital One's performance on this survey is particularly impressive when you consider that its $351 billion in assets means it's a fraction of the size of JPMorgan Chase.

One thing to note about the survey, however, is that JPMorgan Chase received a peculiar number of customer ratings -- 1.1 million, to be precise. No other bank, not even Bank of America, got more than 330,000. It's hard say what accounts for this disparity. Maybe JPMorgan Chase directed customers to the survey? Maybe its employees participated overwhelming in it? Who knows?

But either way, the one thing that is certain is that, based on the number of users alone, JPMorgan Chase has the most popular banking app in the United States.