When (and How) to Add Late Fees in Australia

Late-payment interest exists for one reason: the party who has not been paid should not be worse off because the party who owes the money chose not to pay on time. In commercial lending, a borrower pays interest for the use of money. When a client pays 60 days late, they have effectively borrowed from you interest-free. A late-fee clause corrects that — but only if it is in place before the invoice is issued.

The legal basis for late fees in Australia

There is no general statutory right to interest on overdue commercial invoices in Australia (unlike in the UK, which has the Late Payment of Commercial Debts (Interest) Act). You need a contractual right. That right comes from:

Your terms of trade — the most reliable method. A signed (or accepted) terms of trade document establishes the right to interest for all transactions under that agreement.
Your contract — project-specific contracts can include a late-payment interest clause.
Your invoice — placing a late-fee clause on the invoice itself has weaker legal standing (it is not necessarily agreed upfront), but it is better than nothing and may be enforceable if the client has a consistent history of accepting invoices with that clause.
Your quote or proposal — if the quote or proposal is accepted in writing and includes the late-fee terms, this is a valid contractual basis.

What rate to charge

There is no legislatively mandated rate for commercial late-payment interest in most Australian states. Common approaches:

RBA cash rate + margin: The Reserve Bank of Australia cash rate, plus a fixed margin of 6–10 percentage points. As at mid-2026, the RBA cash rate is [check current rate]. A clause at RBA + 8% is common and commercially fair. The margin should reflect your cost of funds and the administrative burden of chasing overdue accounts.
Fixed rate per annum: A fixed rate such as 12% per annum (approximately 1% per month, or 0.033% per day) is simpler to calculate and communicate. This is effective and easy for clients to understand.
Penalty Interest Rate (VIC): Victoria's Penalty Interest Rates Act 1983 sets the rate for court-ordered interest — this is often used as a reference rate for contractual interest. As at July 2026, check the current Victorian penalty interest rate.
Administration fee (flat): Some businesses charge a flat administration fee (e.g. $50–$150) per overdue reminder letter, in addition to or instead of interest. This must be stated in your terms. It covers administrative costs rather than compensating for the time value of money.

How to calculate late-payment interest

Most late-payment interest clauses accrue daily. The formula:

Daily interest = Outstanding amount × (Annual rate ÷ 365)

Example: $10,000 outstanding × (12% ÷ 365) = $3.29 per day

After 30 days: $10,000 + (30 × $3.29) = $10,098.63

After 90 days: $10,000 + (90 × $3.29) = $10,295.89

Use the Merion late payment calculator to calculate the exact interest accruing on any overdue invoice.

How to charge late fees — the right process

Establish the contractual right before credit is extended — include a late-payment clause in your terms of trade, quote or contract. Get it signed or accepted in writing.
State the late-fee clause on every invoice — even if your terms are already agreed, a reminder on the invoice is good practice. Example: "Overdue amounts accrue interest at 12% per annum from the due date."
Calculate interest from the due date — not from the date of the first reminder or the date you noticed it was overdue. Interest accrues from the day after the due date.
Issue an interest invoice separately — do not just add interest to the principal invoice. Issue a separate tax invoice (or debit note) for the interest amount. This is also the correct treatment for GST purposes.
Apply interest to the total outstanding — including previous interest — if your terms allow compound interest, apply interest to the principal plus accrued interest. If your terms specify simple interest, apply it to the principal only.

When to actually charge late fees

Having the right to charge late fees is different from when it makes sense to do so. Practical guidance:

First offence, short delay: mention the interest clause in your first reminder as a reminder of your rights, but do not invoice for it unless the delay continues.
Repeat late payer or significant delay: charge interest. Issue the interest invoice alongside the firm reminder. This is a legitimate commercial claim and a signal that you are serious.
Disputed invoice: do not charge interest on genuinely disputed amounts until the dispute is resolved.
Pre-litigation: include all accrued interest in any formal demand letter and any subsequent court claim.

Late fees and the client relationship

A reasonable late-fee clause, communicated clearly at the start of the relationship, rarely damages a good client relationship — because good clients pay on time. The clients who push back on late-fee clauses are often the same ones who pay late. That is useful information.

The most effective use of a late-fee clause is as a deterrent. An invoice that states "interest accrues at 12% per annum from the due date" creates a financial incentive to pay on time — which is the goal.

Frequently asked questions

Can I charge late fees without warning?

No. You must have a contractual right to charge late fees — either in your terms of trade, the invoice itself or a signed agreement. You cannot impose late fees retrospectively or without prior notice. The most reliable approach is a signed terms of trade document before any credit is extended.

What interest rate can I charge on overdue invoices?

There is no statutory minimum or maximum rate for commercial late-payment interest in Australia (outside of specific industries). The rate must be stated in your contract. Common practice is the RBA cash rate plus a margin of 6–10 percentage points. The Penalty Interest Rates Act (VIC) and similar instruments set a reference rate for court-ordered interest — this is distinct from contractual interest.

Is late-payment interest taxable income?

Yes. Interest received on overdue invoices is taxable income and should be recorded as such. Issue an invoice or credit note for interest charged and account for it in your BAS.

Can I charge late fees to a government client?

Commonwealth and state government agencies have specific payment policies. The Commonwealth Government's supplier payment policy requires payment within 30 days (20 days for small businesses). Some state government contracts include interest provisions. Check the terms of your specific government contract.

Can I charge both a flat late fee and interest?

Yes, if your terms allow for both. Some businesses charge an administration fee for processing overdue accounts (e.g. $50 per reminder letter) plus interest on the principal. Ensure your terms are clear that both apply and are not alternative remedies.

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