Late Payment Fee Calculator

About this calculator

A late payment fee is a penalty charged on an overdue invoice, typically calculated as a percentage of the outstanding balance — either a flat one-time charge or accruing per day or per month the payment remains unpaid, depending on the terms stated in the original invoice or contract. Businesses set the rate and grace period upfront (commonly stated in the invoice's payment terms, like 'Net 30, 1.5% monthly late fee'), so the calculation depends entirely on those agreed terms rather than any fixed legal rate.

Freelancers, small businesses, landlords, and B2B vendors use late fees to encourage on-time payment and to compensate for the cost of delayed cash flow, while accounts-receivable teams calculate them to know exactly what to bill a client who's paid late.

This calculator takes the overdue balance, the late fee rate, and the number of days or periods late and returns the fee owed.