U.S. travelers could end up paying extra, unexpected fees on their debit or credit cards, including for transactions that occur abroad and withdrawals at out-of-network ATMs. The biggest banks here charge customers as much as $3 to use an out-of-network ATM in the country and as much as $5 to use one beyond U.S. borders. Foreign transaction fees, meanwhile, will cost the spender 1 percent to 3 percent of the total purchase price. Card users can reduce the impact of both ATM fees and foreign-transaction fees by planning ahead. They should find out if their bank has international ATMs or is part of an extended ATM network as well as if it has branches or partner banks overseas. Customers also should alert their bank before they plan to leave the country; otherwise an overseas purchase could trigger a fraud alert and freeze the account.