Many Americans struggle to pay down their credit card debts, a challenge exacerbated by the holidays when credit-card spending balloons. The Federal Reserve estimates that nearly half of U.S. households are unable to pay their credit card bills in full each month. These households owe more than $800 billion in card debt—an average of more than $15,000 per household spread across an average of four credit cards. To pay it down consumers must regularly decide how to allocate repayments, above minimum requirements, among their different accounts.