Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Calculate a late payment fee based on a periodic rate and how many periods overdue.
This tool calculates a late fee that accrues per period (e.g. per month) an invoice remains unpaid past its due date -- the standard late-fee accrual structure used in freelance and B2B invoicing.
Enter the invoice amount, the late-fee rate per period, and how many periods overdue. Fee amount and total due appear instantly.
Late Fee = Invoice Amount × (Rate % per Period) × Periods Late
The calculator starts with an invoice of 1,000, a rate of 1.5 percent per period, and 2 periods late. The fee is 1,000 times 0.015 times 2, which is 30, so the total due is 1,030. Each additional period adds the same 15, because the fee is calculated on the original invoice amount only.
The same structure works for other time units as long as the rate and the count use the same unit. For example, if your terms charge 0.05 percent per day on an invoice of 2,400 and the invoice is 45 days overdue, the fee is 2,400 times 0.0005 times 45, which is 54. Entering 0.05 as the rate and 45 as the periods gives that result. Mixing units, such as a monthly rate with a number of days, is the most common way to get a wrong answer.
This calculator uses simple accrual: the fee grows in a straight line with the number of periods, and the running fee is never added back into the base for the next period. If your agreement specifies compound interest, where each period charges on the previous balance plus earlier fees, the real amount would be somewhat higher for long delays and this tool would understate it. The tool also does not cap the fee, so entering a very large number of periods will produce a very large fee even where a legal maximum might apply.
Total due is the original invoice amount plus the fee, in US dollar formatting. If the client has already made a partial payment, enter the outstanding balance as the invoice amount instead of the original total, or the fee will be overstated.
Commonly 1-1.5% per month in freelance/small-business invoicing, though this varies by contract and jurisdiction -- always state your late-fee terms clearly on the original invoice.
No. It is a simple calculation on the invoice amount, so every period adds the same amount. Compounding terms would produce a larger figure than this tool shows.
Yes, as long as the periods field is also in days. The tool does not care about the time unit; it multiplies the amount, the rate percentage and the number of periods.
Enter the remaining unpaid balance as the invoice amount so the fee is based on what is actually overdue.
Many places regulate late fees or interest on overdue payments, and the rules differ widely. Check your local government guidance or consult a legal professional before setting or enforcing a rate.
Reference: Consumer Financial Protection Bureau