Interests on Credit
When a debtor has a credit balance with the National Treasury's collection agency the amount bears interests in accordance with the Act on the refund of overpaid taxes and levies. According to this Act, the credit only bears interest if it has not been paid within 30 days. In case of non-payment within that time frame, the interests start accumulating from the day the overpayment was made until the day it is paid back.
The interest rate of credit balances at any given time is determined by the Central Bank of Iceland.