(Reuters) – U.S. borrowers are increasingly missing payments on home equity lines of credit they took out during the housing bubble, a trend that could deal another blow to the country’s biggest banks.

The loans are a problem now because an increasing number are hitting their 10-year anniversary, at which point borrowers usually must start paying down the principal on the loans as well as the interest they had been paying all along.

More than $221 billion of these loans at the largest banks will hit this mark over the next four years, about 40 percent of the home equity lines of credit now outstanding.

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