Interest on late payments is interest that can be added to lapsed bills. Interest on late payments can be added after the expiration date but no sooner than 30 days after the bill being issued. The interest is updated each day until the bill has been paid. 

Interest on late payments are regulated in the Swedish Interest act. If nothing else has been agreed, interest on late payments is 8.0% per year plus the current central bank interest rate, which currently means total interest is usually between 8 and 9%. Be aware that interest on late payments stops being applied to an invoice that has been partly paid