Русско-англо-русский юридический словарь

A penalty interest rate is generally charged when you are in some sort of default under your credit card agreement, most often by paying late. (Yahoo News UK)

The consultation sought to explore the merits of alternative sanctions: charging a penalty rate of interest (penalty interest), and revising and aligning existing late payment penalty provisions. (parliament.uk)

A default rate refers to the interest rate that is applied to a loan or credit agreement when the borrower fails to make payments according to the terms of the contract. The default rate is typically higher than the standard interest rate and is meant to compensate the lender for the increased risk and administrative burden caused by the borrower’s failure to pay on time. (Cobrief)