It’s no secret that mobile banking customer numbers are growing, and it’s even no secret how many customers the big banks have.

Well, that’s not exactly true. It’s no secret about how many mobile users Wells Fargo & Co., JPMorgan Chase & Co., and Bank of America Corp. have. Citigroup, however, is another story. The New York-based bank does not publicize its mobile numbers. Can we make a good-faith estimate nonetheless? Let’s take a look:

Wells Fargo
Brian Pearce, head of the retail mobile channel at Wells Fargo, told Bank Innovation last November  that the San Francisco-based bank had “more than 9 million” mobile users. Wells Fargo is the largest holder of FDIC-insured deposit accounts in the nation, but was a little late to the starting line with mobile offerings. (Bank Innovation explored why here.) With 94.7 million checking account holders, Wells Fargo has about 9 million mobile users.

JPMorgan Chase
In October 2012 Bank Innovation reported that JPM had 9.8 million mobile users. The bank itself reported “over 10 million” in a September 2012 press release for the Windows mobile version of its app. In January 2013, Chase disclosed that it had 12.4 million active mobile users.

In March 2012 Ravi Acharya, SVP of product management for online and mobile at JPM, claimed that the bank had 15 million mobile users, but presumably 5 million or so of these were not active. So let’s put Chase, with about 45.5 million FDIC-insured deposit accounts, at 12.4 million mobile users.

Bank of America
David Godsman, senior vice president of online and mobile solutions at BofA, cited 12 million as the number of Bank of America mobile users in December 2012. More recently, 12 million was stated as a fast-approaching goal for BofA. Regardless, we’ll put the mobile user customer base at 12 million for Bank of America, which maintains 66.5 million deposit account holders.

Citibank
But what about at Citibank? Citi is the only of the four major banks to withhold the count for its mobile users in the US. However, we’ve done a lot of work here at Bank Innovation, so we can present an estimate. Let’s start with what we know. As of the end of last September, Citi had 1.1 million mobile users in Asia. Citi was added around 250,000 new mobile users a year there, and since the rate of adoption is probably heading higher, we’ll put Citi’s Asia mobile userbase at 1.2 million today. The worst rate of user adoption among the three banks listed above is at Wells Fargo, where 9% of its customer base is a mobile user. Citi’s mobile adoption in Asia is around 3.5%, and Citi certainly hasn’t been aggressive about its mobile apps. You can get a sense for mobile prowess in the number of comments the apps at the four banks get on iTunes, as of today.

Source: Apple

It would not make sense to assume a higher mobile adoption rate at Citi than at Chase, considering how vanguard has been Chase with remote deposit capture and advertising its RDC and mobile app. Assuming our readers take our estimate for adoption at Citi with a grain of salt, we estimate Citi’s at possible around 7%. (Considering the Asia numbers, we think this is a charitable assumption.) Assuming that rate, we think Citi has around 2.9 million mobile users in the US.

As to what defines a mobile user vs. an active mobile users — we’ll save that for another post.