Invoice late fee
Free invoice late fee calculator
Enter the unpaid invoice balance, an agreed flat fee or percentage rate, and the number of charge periods to estimate the late fee and updated amount due.
Free, no sign-up, and the entered values stay in your browser.
How the calculation works
Enter the unpaid invoice balance, an agreed flat fee or percentage rate, and the number of charge periods to estimate the late fee and updated amount due.
Late fee = flat fee × periods + unpaid balance × percentage rate × periods. Updated balance = unpaid balance + late fee.Charge a late fee only when the customer agreed to the term and applicable law permits it. Check local notice, rate and compounding rules before updating an invoice.
Calculate the fee only after checking the agreement
A late-fee calculation should match the written payment terms, applicable law and the dates used. Keep the original balance separate from the fee and current total.
- Check written terms
- Use the contractual due date
- Show the fee separately
- Update partial payments first
Confirm the fee is authorized
Check the signed contract, invoice terms and local rules before applying a fixed fee or percentage. Do not add a fee that was never disclosed.
Use the correct overdue period
Start from the contractual due date and account for any grace period. State whether a percentage applies once, monthly or under another schedule.
Show the calculation clearly
Keep the original invoice balance, fee basis, rate, overdue period and resulting fee as separate lines so the customer can verify the amount.
Record payments and adjustments
Partial payments, credits, disputed work and prior fees can change the eligible balance. Update the record before sending a reminder or revised statement.
Late-fee calculation examples
Percentage fee
eligible balance × rateUse the authorized balance.
Fixed fee
stated contract amountDo not compound unless permitted.
Updated total
balance + allowed feeKeep payments and credits current.
Payment-term references
Questions about free invoice late fee calculator
Can I add a late fee to any overdue invoice?
No. The fee should be supported by the accepted contract or invoice terms and allowed by the law that applies to the transaction.
Should a late fee be flat or percentage based?
Use the method stated in the agreed payment terms. A flat charge is a fixed amount per period, while a percentage charge changes with the unpaid balance.
Does this calculator compound late fees?
No. The percentage is applied to the original unpaid balance for each entered period. It does not charge interest on earlier late fees.
Review the terms and follow up payment
Set clear invoice payment terms
State when and how to pay, with any agreed late fees that apply to the transaction.
Open resource →Follow up outstanding invoices
Check the balance and earlier messages before sending a payment reminder.
Open resource →Track invoice payment status
Record invoice amounts, received payments and balances, and organize unpaid invoices by due date.
Open resource →