How much is this overdue invoice costing me?
Counted from the due date, not the invoice date.
Whatever your contract says. 8% over base is the usual statutory figure in the UK and EU.
A flat charge your contract allows on top of interest.
Total you can now claim
$2,013.15
30 days at $0.44 a day
You can only charge interest your contract provides for, or that the law in your country allows by default. Put the rate in the contract before the invoice, not after.
Free Late Payment Fee Calculator
Enter the invoice, how many days late it is and the rate your contract allows, and see the interest accrued, the total you can claim now, and what it grows to if it runs another month.
Built by Slashit · Last updated 27 September 2026
What is the late payment fee calculator?
A late payment fee calculator works out what an unpaid invoice has cost you in interest, and what you are entitled to claim. Late payment is the most common cash-flow problem in freelance and agency work, and most people never charge interest on it — partly out of awkwardness, and partly because they have never worked out the number. Having the figure changes the conversation: 'the invoice is overdue' is easy to ignore, while 'the invoice is now £2,013.15 including statutory interest, rising by 44p a day' is specific, unemotional and much harder to keep ignoring. One condition matters: you can only charge what your contract provides for, or what the law in your country allows by default.
How our free late payment fee calculator works
Enter the invoice
The amount outstanding, excluding anything already paid.
Count from the due date
Days overdue runs from the payment due date, not the date you sent it.
Use your contract's rate
Whatever you agreed. Where nothing was agreed, many countries set a statutory default.
See what you can claim
Interest so far, the total now, the daily rate, and where it lands in another month.
What can you use the late payment fee calculator for?
The second reminder
The first is polite. The second carries a number, a daily rate and a date.
Setting a contract rate
Decide the interest rate when you write the contract, not when you are already angry.
Deciding whether to escalate
Seeing the real cost of waiting helps you judge when to stop being patient.
Who uses our free late payment fee calculator?
Freelancers
Chasing an invoice that is weeks past due without knowing what to ask for.
Agencies
Where several overdue invoices at once become a genuine cash-flow problem.
Small businesses
Applying a late payment policy consistently instead of case by case.
Anyone writing a contract
Deciding what interest rate to put in before it is ever needed.
Why use the late payment fee calculator?
A specific number
Far harder to ignore than 'please pay when you can'.
Shows the daily cost
A per-day figure creates a reason to pay today rather than next week.
Projects forward
Shows what another month of silence adds.
Tips for getting the best results
Put the rate in the contract
Interest you never agreed is hard to enforce. One line in the payment terms is enough.
Send the calculation, not just the total
Amount, days, rate, daily figure. It reads as process rather than as a threat.
Waive it if they pay now
Offering to drop the interest on immediate payment works more often than charging it does.
Check your country's statutory right
Many countries give businesses an automatic right to interest on late commercial payments even without a contract term.
Frequently asked questions
Can I charge interest if my contract does not mention it?
Often yes, but it depends entirely on where you are. Several jurisdictions, including the UK and EU member states, give businesses a statutory right to interest on late commercial payments regardless of the contract. Check your own country before relying on it — and put a clause in the contract so the question never arises.
What rate should I use?
Whatever your contract specifies. Where there is none, statutory rates are often defined as a fixed percentage above a central bank base rate — 8% above base is a common figure in the UK and EU.
Is it simple or compound interest?
This calculates simple interest on the outstanding amount, which is the usual approach for commercial late payment and the more defensible one to put in a letter.
Will charging interest cost me the client?
A client who pays 60 days late is already costing you. In practice, most either pay promptly once a number appears or were never going to pay at all — and both outcomes are more useful than silence.
Is this legal advice?
No. It is arithmetic. What you are entitled to claim depends on your contract and your jurisdiction.
