Invoice Late Fee Calculator
Work out a late fee or interest charge on an overdue invoice.
Updated . Runs in your browser; nothing you type is stored.
How late fees on invoices work
Late payment is one of the biggest headaches of freelancing. A clear late fee, written into your contract and printed on every invoice, gives clients a reason to pay on time. The two common approaches are a percentage interest charge, usually quoted per month, and a one-off flat fee. Some businesses use both.
This calculator applies the monthly rate day by day, so a payment 45 days late is charged for exactly 45 days rather than a full two months. That is the fairest method and the easiest to explain to a client.
The formula
Daily rate = monthly rate × 12 ÷ 365
Interest = invoice amount × daily rate × days overdue
Total due = invoice amount + interest + flat fee
Worked example
A $2,000 invoice is 45 days late and your terms say 1.5% per month. That is 18% a year, or about 0.0493% a day. $2,000 × 0.000493 × 45 ≈ $44.38 of interest, so the client now owes $2,044.38.
Before you charge a late fee
- Put it in writing first. A late fee is easiest to enforce when it was in the contract or on the invoice before the work began.
- Check local rules. Many states and countries cap the interest you may charge or set a statutory rate. Confirm what applies to you.
- Send a friendly reminder a few days before and after the due date. Most late payments are simply forgotten.
Frequently asked questions
What is a typical late fee?
A monthly rate of 1% to 1.5% is common, as is a flat fee of $25 to $50 for small invoices. Always check the legal limit where you and your client are based.
Should interest be simple or compound?
Simple interest, as used here, is the norm for invoices and is easier for clients to understand.
Is this legal advice?
No. This tool only does the arithmetic. Rules on late fees differ by location, so check them or ask a professional before enforcing a fee.