Mobile banking adoption tripled in a year, to 21% of consumers, among America's youngest adults, according to a survey that Mercatus LLC is expected to release today.

"We're approaching an inflection point where banks are no longer just testing mobile banking," said Robert B. Hedges Jr., managing partner of the Boston consulting firm. "It will be table stakes, where consumers are going to expect banks to offer these services to them."

He predicted that the change would occur in the next year to 18 months, when consumers begin making decisions about where to bank based on the availability of mobile services.

But adoption will likely be strongest among younger consumers, he said. Consumers above age 50 show less interest in mobile banking than younger people.

In a June survey of 1,166 people, 21% of respondents age 18 to 25 said they had accessed account balances, paid bills or transferred money with a mobile phone, up from 7% in a May 2008 survey.

In the 25-to-34 age group, 16% said they used their phones for banking, compared with 7% a year earlier. Adoption grew by 2 percentage points among the next three age groups, to 12% among those 35 to 44, to 6% among those 45 to 54 and to 7% among those 55 to 64. For respondents 65 or older, use was unchanged at 3%.