Yes, you can charge interest or a late fee on overdue invoices in Australia — but only if it was agreed in advance. The charge must be set out in your quote, contract or terms and accepted by the client before the work starts, and it has to be reasonable rather than a punishment. You can't spring a fee on a client after the invoice is already late. Here's how to do it properly.
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The golden rule: agree it in advance
A late fee or interest charge is only enforceable if the client agreed to it before you did the work. That means putting it in writing — in your quote, your engagement letter, your standard terms and conditions, or your service agreement — and having the client accept those terms. Restating it on the invoice itself is good practice, but the invoice alone isn't enough; by the time you issue an invoice, the agreement is already made.
If you never mentioned late fees and an invoice goes overdue, you generally can't add one retrospectively. What you can do is chase the debt through reminders and, if needed, escalation — covered in our guide on how to chase overdue invoices. For next time, bake the terms into your paperwork.
What's a reasonable rate?
The charge has to be a genuine estimate of the cost late payment causes you — not a penalty designed to punish. Two common, defensible approaches:
- Interest at around 1.5% per month (roughly 18% per year) on the outstanding balance, typically calculated daily from the due date until the invoice is paid. This is a widely used benchmark for small businesses.
- A modest flat administration fee — for example a set dollar amount added once an invoice passes a certain number of days overdue, reflecting the real admin cost of chasing it.
Whichever you pick, keep it proportionate. Courts and tribunals can refuse to enforce a charge that looks like a penalty rather than genuine compensation, so an eye-watering rate can leave you worse off than a reasonable one. When in doubt, err on the modest side — the point is to encourage prompt payment, not to profit from lateness.
How to word your terms
Clear, specific wording works best. A simple clause you can adapt for your quote and terms:
"Payment is due within 14 days of the invoice date. Overdue accounts may incur interest at 1.5% per month (calculated daily) on the outstanding balance from the due date until paid in full."
For a flat fee instead:
"Accounts more than 14 days overdue may incur a $25 late administration fee."
Then repeat a short version in the notes or footer of each invoice — for example, "Overdue accounts may incur interest at 1.5% per month per our terms." Consistency between your agreement and your invoice matters. If you're still setting up your invoicing, our guides on how to write an invoice and invoice payment terms in Australia cover where these details belong.
The GST grey area
Whether GST applies to a late fee is genuinely unsettled and depends on how the charge is structured. In broad terms, the ATO treats a genuine penalty for late payment as not being consideration for a supply — meaning GST may not apply to it, even if the underlying goods or services were taxable. But if the "late fee" is really an additional charge for the supply, the answer can differ.
Because the distinction is technical and fact-specific, don't guess. Check the ATO's guidance on penalties and adjustments, and confirm the correct treatment with your accountant before you start adding GST to late fees. Getting this wrong on a tax invoice can create reporting headaches, and the amounts usually aren't worth the risk of doing it incorrectly. If you're registered for GST, our post on tax invoice requirements in Australia explains what a compliant invoice must show.
Should you actually charge late fees?
Having a late-fee clause is often more valuable as a deterrent than as a revenue line. Many businesses quote the clause in their terms, mention it once when an invoice is overdue, and then waive it the moment the client pays — because the relationship is worth more than the fee. Used that way, it's a polite lever: "our terms allow for interest, but I'm happy to waive it if this is settled by Friday."
Whatever you decide, the sequence is the same: agree the terms up front, keep the rate reasonable, state it clearly on every invoice, and confirm the GST position with your accountant. Do that and a late-fee policy becomes a quiet incentive for clients to pay you on time.
This article is general information, not legal, tax or financial advice. Rules and GST treatment can change — check the ATO and business.gov.au, and speak to a qualified accountant or adviser for your situation.
Frequently asked questions
Can you charge interest on overdue invoices in Australia?
Yes, you can charge interest or a late fee on overdue invoices, but only if it was agreed in advance — stated in your quote, contract or terms and accepted by the client before the work started. You cannot add a fee out of the blue after an invoice is already late.
What is a reasonable late payment interest rate?
A common approach is around 1.5% per month (roughly 18% per year) on the outstanding balance, or a modest flat administration fee. The charge must be a genuine reflection of your costs, not a penalty — excessive fees can be challenged and may be unenforceable.
How do I add a late fee clause to my invoice terms?
Include a clear line in your quote and on the invoice, for example: "Overdue accounts may incur interest at 1.5% per month on the outstanding balance, calculated daily from the due date." Make sure the client agrees to these terms before you begin work.
Do I charge GST on a late payment fee?
It's a grey area. The ATO generally treats a genuine penalty for late payment as not being consideration for a supply, so GST may not apply. But treatment depends on how the fee is structured — check the ATO's guidance and confirm with your accountant before deciding.
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