New York | Four in 10 American adults wouldn't be able to cover an unexpected $US400 ($580) expense with cash, savings or a credit-card charge that could be quickly paid off, a new Federal Reserve survey finds.

About 27 per cent of people surveyed would need to borrow or sell something to pay for such a bill, and 12 per cent would not be able to cover it at all, according to the Fed's 2018 report on the economic well-being of households, which was released on Thursday (Friday AEST).