Invoice Late Fee Calculator
Enter your invoice amount, due date, and late fee terms and get the exact amount to charge your client for a late payment.
Getting paid late is frustrating enough. Figuring out what to charge for it shouldn’t add to that. Whether your contract specifies a flat fee, a monthly percentage, or daily interest, this calculator gives you the exact number to put on the invoice — no spreadsheet required.
Invoice Details
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Enter your details and click Calculate
Your late fee total will appear here
How to Use It
Step 1 — Enter your original invoice amount
This is the amount your client was supposed to pay, before any late fees.
Step 2 — Set the due date and payment date
The calculator uses these two dates to figure out how many days late the payment is.
Step 3 — Choose your late fee type
Check your contract. Most freelancers and small businesses use a monthly percentage (1.5% is standard). Some use a flat fee. Others charge daily interest.
Step 4 — Enter your grace period
If your contract allows a grace period before fees kick in, enter it here. If not, leave it at zero.
Step 5 — Read your total
The calculator shows you the fee amount and the new invoice total to send your client.
How the Math Works
For a monthly percentage fee:
Days Late = Payment Date − Due Date − Grace Period
Months Late = Days Late ÷ 30
Late Fee = Invoice Amount × (Monthly Rate ÷ 100) × Months Late
New Total = Invoice Amount + Late Fee
For a flat fee:
New Total = Invoice Amount + Flat Fee Amount
For daily interest:
Late Fee = Invoice Amount × (Daily Rate ÷ 100) × Days Late
New Total = Invoice Amount + Late Fee
Who This Is For
Freelancers and consultants who include late fee clauses in their contracts
Small business owners invoicing clients or customers
Agencies managing net-30 or net-60 payment terms
Anyone who needs to calculate interest on an overdue invoice before resending it
Tips for Handling Late Payments
Put your late fee terms in writing before you start work
A late fee clause only holds up if it’s in your contract or on your invoice. Add it before the project starts, not after a client goes silent.
1.5% per month is the industry standard
Most freelancers and small businesses use 1.5% monthly (18% annually). It’s common enough that clients recognize it and high enough to motivate faster payment.
Send a reminder before the due date
A quick heads-up two to three days before the invoice is due cuts late payments significantly. Most late payments aren’t intentional — clients just forget.
Be consistent about enforcing fees
If you waive late fees every time, clients learn they don’t matter. Enforce them consistently or remove them from your contracts entirely.
Know your state’s legal limits
Some states cap how much interest you can charge on overdue invoices. If you’re dealing with large invoices or repeat offenders, check your state’s usury laws before charging.
Consider early payment discounts instead
Some businesses get better results offering a 2% discount for payment within 10 days (net-10) rather than penalizing late payment. Both approaches work — pick the one that fits your client relationships.