Invoice Late Fee Calculator
Work out the late fee and total now owed on an overdue invoice.
Reviewed by the ToolNestr Editorial Team — July 2026
Late fee formulas
The calculator supports five common late-fee structures. Which formula applies depends on whether you charge a percentage or a flat fee, and whether the fee is applied once, per month, or per day.
Percentage — one-time
Late Fee = Invoice Amount × (Rate / 100)
A single percentage charge applied once regardless of how late the payment is.
Percentage — per month
Late Fee = Invoice Amount × (Rate / 100) × (Days Overdue / 30)
A monthly percentage prorated by the number of days overdue. Each 30-day block incurs a full month's fee.
Percentage — per day
Late Fee = Invoice Amount × (Rate / 100) × Days Overdue
A daily percentage that accumulates linearly over each day the invoice is late. Adds up quickly for long delays.
Flat fee — one-time
Late Fee = Flat Fee Amount
A single fixed charge applied once, regardless of how overdue the invoice is.
Flat fee — per day
Late Fee = Flat Fee Amount × Days Overdue
A fixed amount charged per day that the invoice remains unpaid. The total fee grows with each passing day.
Worked example
Invoice amount: $1,000 | Fee: 1.5% per month | Days overdue: 30
Same invoice with a $25 flat fee charged per day for 10 days:
Use cases
Freelancers chasing invoices
If you invoice clients on net-30 or net-60 terms, a late fee policy encourages prompt payment. Use this calculator to determine the exact fee before sending a reminder or an updated invoice — it gives you a confident number to reference.
Small businesses setting policy
When drafting your payment terms, compare different fee structures side by side. A 1.5% monthly fee versus a $10 flat fee per day may look similar on paper but produce wildly different totals depending on the invoice amount and delay length.
Verifying vendor charges
Received an invoice from a supplier that includes a late fee line item? Plug the numbers into this calculator to verify their math. A surprising number of errors come from miscalculated prorated periods or incorrect fee type application.
Dispute resolution
When a client disputes a late fee, a clear breakdown of the calculation helps resolve the disagreement. Show the formula, the inputs, and the resulting fee — transparency goes a long way toward maintaining the business relationship.
Tips for charging late fees
Check local legal caps
Many jurisdictions cap the maximum late fee you can charge. In the US, usury laws vary by state — some cap interest at 10–12% per year, while others allow higher rates for commercial invoices. Research your local regulations before setting a rate to ensure your fee is enforceable.
State the policy up front on the invoice
A late fee is only enforceable if the client agreed to it beforehand. Include a clear line item on every invoice: "Late payment: 1.5% per month on amounts overdue beyond 30 days." This makes the fee a contractual term rather than a surprise penalty.
Be consistent but reasonable
Apply the fee consistently to all clients to avoid claims of unfair treatment. At the same time, consider waiving the fee once as a courtesy for long-standing clients who made an honest mistake — preserving the relationship is often worth more than a single late fee.
Send a reminder before charging
A polite reminder email a day or two after the due date is often enough to collect payment without ever needing to apply the fee. Set the expectation that fees will be applied automatically after a grace period, and most clients will pay on time.
Related tools
Frequently asked questions
What is a typical late fee?
Commonly 1–2% of the invoice per month, or a small flat fee — but it must be stated in your terms.
Is a late fee legal?
Usually yes if stated in your contract or invoice, but many jurisdictions cap the rate — check local rules.
Does the fee compound?
This tool charges simple interest on the original amount; it does not compound the fee on the fee.
Should I charge per day or per month?
Per month is more common and feels fairer; per day adds up faster for long delays.
What if my client never pays?
Late fees encourage prompt payment. For chronic non-payment, consider a collections process or legal action.
Sources & references
This tool uses standard formulas and reference values from:
- • IRS — federal tax brackets, standard deduction and instructions for the tax year. irs.gov
- • U.S. SEC — Investor.gov, compound interest and investment reference material. investor.gov
- • Official national tax authority for the relevant country — link the exact rate schedule used.
Estimates only, not tax or financial advice. Confirm current figures with the official source or a qualified professional.