So now we know.

Brian Moynihan, the chairman and chief executive of Bank of America, disclosed yesterday the rate of savings the megabank is getting from its customers shifting to mobile banking for services: 90%.

Indeed, Moynihan said on an investor call yesterday that mobile “is one-tenth the cost relative to processing of financial centers and more convenient for customers.”

Deposits via mobile devices accounted for 14% of BofA’s total consumer deposit transactions last quarter. About $504 billion of non-investment deposits came through BofA’s consumer banking channel in the third quarter, which means around $71 billion of deposits arrived via mobile device.

Interestingly, BofA’s noninterest expenses, however, have not declined much in recent quarters, sitting at around $12.7 billion, excluding litigation. Moynihan acknowledged this, saying yesterday, “We continue to be able to hold the core expenses flat while we make the investments pay.”

That is, “flat” despite 17.4% year-over-year growth in active mobile users.

Learn more about mobile banking innovation at Bank Innovation Israel, Nov. 10-11 in Tel Aviv. Request an invitation here.