Invoice Late Fee & Interest Calculator
Calculate interest and late fees on an overdue invoice — by annual rate or monthly percentage, with a fixed fee — for the days it's overdue.
How to use
- 1Enter the invoice amount, due date and payment (or today's) date.
- 2Enter your contract's interest rate and any fixed late fee.
How it's calculated
Interest = amount × annual rate × days late ÷ 365 (or monthly rate × days ÷ 30). Total due = amount + interest + fixed fee.
Frequently asked questions
Can I charge interest on late invoices?
If your contract or terms allow it, and within legal limits. In the UK, the Late Payment Act allows 8% above the Bank of England base rate on B2B invoices; many US states cap rates.
What's a common late fee?
1–1.5% per month is common in US business terms. Always state it on the invoice and in your contract.
Does interest compound?
Usually not on invoices — this calculator uses simple interest.