How to use this late fee calculator
- Enter what the client still owes. If they paid part of the invoice, enter only the unpaid balance.
- Set the due date and payment date. Leave “Not paid yet” ticked to see the fee as of today, or untick it to price a fee on an invoice that was paid late.
- Copy your terms. Choose the fee method, rate, grace period and any cap exactly as your contract or invoice states them.
- Use the output. Check the month-by-month table, then copy the result, the clause or the notice email. Copy link saves the calculation as a shareable URL.
How late fees on invoices work
A late fee compensates you for being paid after the agreed date. It is a fixed charge, a percentage of the unpaid balance that grows the longer the invoice stays open (interest), or a mix of both. Three details decide the final number, and they are where most disagreements start:
- The unit. “1.5%” means little until you say per month or per year.
- The start date. The fee usually runs from the due date, or from the end of a grace period if you give one.
- Part months. A partial month can be prorated by day or charged as a whole month.
The calculator counts whole calendar days, so time zones and daylight saving changes never shift the result. A monthly rate is charged per calendar month from the start date. An annual rate accrues daily on a 365-day basis, leap years included.
Common ways freelancers structure late fees
- Monthly percentage, such as 1% to 2% per month on the unpaid balance. Clients understand it, and it scales with the invoice.
- Annual interest rate, accrued daily. Common in formal contracts and on larger invoices.
- Flat fee, charged once when the invoice becomes late. Simple, but it never grows, and on a small invoice paid a few days late it can equal a very high annual rate.
- Flat fee plus a monthly percentage. An immediate nudge plus a cost that keeps rising.
- Grace period and cap. A few days of grace avoids penalising a bank transfer that took an extra day, and a cap such as 10% of the invoice keeps the fee proportionate on long-overdue accounts.
Worked examples
All six use a $2,400 invoice due September 1, 2026 and paid October 18, 2026: 47 days late with no grace period. September 1 to October 1 is one full month, and the remaining 17 days fall in a 31-day month.
| Method | Calculation | Late fee |
|---|---|---|
| 1.5% per month, prorated by day | $2,400 × 1.5% × (1 + 17/31) months | $55.74 |
| 1.5% per month, per started month | $2,400 × 1.5% × 2 months | $72.00 |
| 18% per year, simple | $2,400 × 18% × 47 ÷ 365 | $55.63 |
| 18% per year, compounded monthly | $2,400 × 1.015 × (1 + 1.5% × 17/31) − $2,400 | $56.04 |
| $50 flat fee | Charged once | $50.00 |
| $50 flat + 1.5% per month, by day | $50 + $55.74 | $105.74 |
Monthly: fee = unpaid amount × monthly rate × months late
Annual simple: fee = unpaid amount × annual rate × days late ÷ 365
Compounded: fee = unpaid amount × (1 + annual rate ÷ 12)months − unpaid amount
1.5% per month and 18% per year land a few cents apart, while charging per started month costs the client about $16 more for the same delay. None of these is wrong. What matters is that your terms say which one you use.
How to add a late fee clause to your invoices
- Agree it before the work starts. Put the clause in the contract or proposal the client signs. That makes it a term they accepted rather than a surprise.
- Repeat it on every invoice. A one-line note next to the due date reminds the accounts team that paying late has a cost.
- Be specific. State the rate and unit, when it starts, any grace period, how part months are handled and any cap. The generator above writes this from your settings, as a short invoice note or a fuller contract clause.
- Keep it consistent. Use the same terms in your contract, invoices and reminder emails.
Legal limits vary by country, state and contract
Rules on late fees and interest differ by country, state or province, by whether your client is a business or a consumer, and by what your contract says. Some places cap interest rates or late charges, some restrict flat fees, and some, including the UK and the EU, give businesses a statutory right to interest and compensation on late business-to-business payments even when the contract is silent. This calculator does not know which rules apply to you, and nothing here is legal advice. Check the current rules for your location and your client's, or ask a lawyer or accountant, before you set a rate. The contract clause includes a sentence limiting the fee to the legal maximum. That is a common safeguard, but it does not make an excessive fee acceptable everywhere.
Should you actually enforce the fee?
The real job of a late fee is to move your invoice to the top of the pile. Charging it is a judgement call:
- Mention it before it applies. A friendly reminder a few days before the due date that restates your terms often gets the invoice paid with no fee at all.
- Waive it strategically. For a good client who is late for the first time, offer to waive the fee if they pay the original amount within seven days. You get paid sooner and keep the relationship. The notice email has an option for this.
- Charge repeat offenders every time. If a client is late again and again, apply the fee consistently and ask for a deposit or upfront payment on future work.
- Bill it clearly. Send the fee as a separate invoice or line item with the calculation attached. The CSV export gives you the schedule.
- Avoid the classic mistakes: charging a fee the client never agreed to, quoting a rate without saying per month or per year, compounding when your terms say simple interest, and setting a flat fee so high it reads as a penalty.
Frequently asked questions
How much should I charge for a late payment?
There is no single right number. Many freelancers charge 1% to 2% per month on the unpaid balance, a small flat fee, or both, usually with a short grace period. Choose a fee large enough to make paying you a priority but proportionate to the invoice, and check that it is allowed where you and your client are based.
Is 1.5% per month the same as 18% per year?
Nearly, but not exactly. Here a monthly rate is charged per calendar month, with a part month prorated by its days, while an annual rate accrues daily on a 365-day basis. On the same invoice the two results usually differ by a small amount. Use whichever unit your contract states.
Can I charge a late fee if it is not in my contract?
Generally, a late fee needs to be agreed before the work starts, in your contract, proposal or written payment terms. Adding one to an invoice that is already overdue invites a dispute. Some countries give businesses a legal right to interest on late business-to-business payments even without a clause, but the details vary, so check the rules that apply to you.
Does the late fee start on the due date or after the grace period?
That depends on your terms. By default this calculator starts charging when the grace period ends. If your terms say a missed grace period means the fee runs from the original due date, tick the option to charge from the due date.
Should late payment interest be compounded?
Most freelance contracts use simple interest, charged on the original unpaid amount only. Compounding adds each month's interest to the balance, so the fee grows slightly faster over long delays. Only compound if your agreement says so.
Is a flat late fee better than interest?
A flat fee is easy to understand and applies straight away, but it does not grow if the client keeps you waiting, and on a small invoice it can amount to a very high annual rate. Interest scales with the amount and the delay. Combining a small flat fee with a monthly percentage gives you both.
What if the client paid part of the invoice?
Late fees normally apply to the unpaid balance only, so enter the amount still owed. If part payments arrived at different times, calculate each stretch separately: the full amount up to the first payment, then the remaining balance after it.
Is my invoice data saved or uploaded anywhere?
No. Everything is calculated in your browser and nothing is uploaded. Your inputs are saved in this browser's local storage so they are there next time, and Reset clears them. Client names and invoice numbers are never added to the shareable link.