The majority of Irish people do not know what interest they are paying on credit-card bills, according to research carried out by the Financial Regulator.
The study found that 45% of credit-card holders do not pay off their bill in full every month, but most have no idea what interest they are paying on the outstanding balance.
Around one-in-10 people involved thought they were paying interest of less than 5% when in fact the average is actually around three times that figure.
The Financial Regulator says rates range from 9.4% at 18.9%, with American Express identified as the most expensive lender.
The Consumers Association says interest rates on credit cards are extremely high and, if people cannot pay the full bill before interest kicks in, they should throw their credit cards away.