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How to Calculate a Late Payment Fee
Chasing late payments is miserable; charging for them fairly should not also be hard. A clear late fee — agreed in advance, calculated consistently — encourages on-time payment and compensates you when it slips. This guide shows the simple math (with a worked example) and the calculator that does it instantly.
Step by step
- Open the Late Payment Calculator and enter the original invoice amount.
- Enter the fee rate — either a monthly percentage (1-2% is common) or a flat fee.
- Enter how many months the payment is overdue.
- Read the fee and the new total due — quote both in your reminder.
Try it now — free, no sign-up
Open the Late Payment Calculator tool
Open the Late Payment Calculator tool
Tips for better results
- A late fee only works if it was in the original terms — add it to every invoice and estimate you send.
- Escalate politely: reminder first, fee notice second. The Payment Reminder Letter generator writes it for you.
- Waive the fee once for a good client who pays immediately — goodwill converts better than penalties.
Frequently asked questions
How is a monthly late fee calculated?
Fee = invoice amount × monthly rate × months overdue. Example: $500 at 2% per month for 1 month = $10 fee, $510 total. For 3 months: $30 fee, $530 total.
What late fee rate is normal?
1% to 2% per month is typical for small businesses, subject to your contract terms and local law — some places cap rates, so check yours.
Can I charge a late fee I never mentioned upfront?
Usually not enforceable. State the fee in your estimates, agreements and invoice terms before the work starts.