How to use the Late Payment Interest Calculator
- Enter the overdue amount and annual rate.
- Enter days overdue and any fixed fee.
- Read interest and total due.
How it works
Interest = Amount × Annual rate × Days overdue ÷ 365. Total due = Amount + Interest + Fixed fee.
Worked example
100,000 overdue 45 days at 12% a year: interest 1,479, so 101,479 is now due.
Good to know
State late-payment terms on the invoice before the due date.
Some jurisdictions cap rates or set statutory fees.
This uses simple interest on a 365-day year.
Frequently asked questions
Multiply amount by annual rate and days late, then divide by 365; add any fixed fee.
It depends on local law; some countries provide statutory interest.
No, this uses simple interest.
Results are estimates for information only and are not financial, tax or legal advice.