Overdue invoice math

Late-Fee Calculator

The exact late-payment fee and new balance to put in your overdue-invoice notice.

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Invoice
Fee method
Monthly %
Annual %
Flat fee
A common, widely-used structure is 1.5%/month (~18%/yr) on the balance. Only charge what your contract or invoice states.
Late fee
—
New balance owed: —
Now send the notice
Invoice Rescue →Generate the late-fee notice email with this figure built in. Cancel & Refund Helper →On the other side of a bill? Scripts to claim refunds & reach a human.
Common questions
What late fee can I actually charge?
Only what your contract or original invoice specified, within local limits. 1.5% per month (~18% annually) is the most common defensible rate. If nothing was agreed, you generally can’t add a fee — but you can still send a firm reminder.
Monthly vs annual %?
Monthly applies the rate for each 30-day period overdue. Annual divides the yearly rate down to the actual days overdue. This tool shows the exact pro-rated figure either way.