Can You Charge Interest On Overdue Invoices In Australia?

Late payments hurt cash flow, increase admin headaches, and distract you from growing your business.

So it’s natural to ask: can you charge interest on overdue invoices in Australia?

The short answer is yes - but only if you set it up properly. The key is having clear, fair terms in place before the work is done or the goods are supplied, and making sure your processes comply with Australian law.

In this guide, we’ll break down what’s legal, what to include in your terms, the rate you can charge, what to do if your current contracts are silent, and the practical steps that reduce late payments in the first place.

Is It Legal To Charge Interest On Overdue Invoices?

Yes. In Australia, you can contractually agree to charge interest on overdue amounts. The catch is you generally need the customer’s agreement upfront - in a signed contract, accepted quote, purchase order that references your terms, or clear online checkout terms.

If you try to add interest after the fact (for example, by unilaterally changing your invoice footer once an invoice is already overdue), you’re likely to run into disputes. Without prior agreement, you usually can’t just impose interest.

Two other legal guardrails to keep in mind:

• Australian Consumer Law (ACL) and Unfair Contract Terms: If you use standard form contracts, terms that are harsh or one-sided can be challenged. Late fees and interest need to be transparent and reasonably protect your legitimate business interests.
• Penalty Doctrine (contract law): Courts may refuse to enforce charges that are out of proportion to the risk or loss (i.e. “punitive”). Reasonableness is your friend.

It’s common and lawful for businesses to include reasonable late payment interest in their terms. Many also use a flat administrative late fee. If you’re weighing up interest versus fees (or both), the key is clarity and proportionality. For more background, see our overview on charging late fees on invoices and broader late payment fee compliance.

What Should Your Late Payment Clause Include?

A solid late payment clause removes ambiguity and reduces disputes. At minimum, include:

• When payments are due: For example, “Payment is due within 14 days of the invoice date.” Your overall invoice payment terms should align with industry norms and your cash flow needs.
• When interest starts: Typically the day after the due date. Some businesses offer a short grace period (e.g. 3-5 days) to account for payment processing delays.
• The interest rate: Express it clearly (e.g. “8% per annum”) and state whether it accrues daily or monthly. Also state if interest is simple or compounding.
• How it’s calculated: A simple sentence like “Interest accrues daily on the overdue amount until paid in full” will do. If compounding, say how often (e.g. monthly).
• Administrative fees (if any): If you use a fixed late fee, specify the amount and when it applies (e.g. “a $25 administration fee may be charged for each reminder letter after an account is 14 days overdue”). Keep it reasonable.
• Cost recovery: If you intend to recover reasonable costs of enforcement (for example, external collection costs), say so. Again, these must be proportionate.
• Suspension rights: If non-payment continues, you may reserve the right to suspend services or withhold delivery until the account is brought up to date.
• Security or set-off (if appropriate): In B2B arrangements, consider whether you’ll require collateral or a right to set off amounts owed. These should be drafted carefully.

These terms typically sit in your Terms of Trade or service agreement. If you offer credit accounts, it’s also common to include them in a signed Credit Application that incorporates your trading terms by reference.

How Much Interest Can You Charge?

There isn’t a single legislated cap for contractual late payment interest across all private transactions in Australia. Instead, the question is what’s reasonable for your industry and circumstances.

Here’s a practical framework:

• Pick an annual rate that is commercially justifiable: Many Australian SMEs fall somewhere in the range of 5-12% per annum for B2B accounts (as a general observation, not a rule). Some benchmark against their own cost of funds.
• Explain the basis: If challenged, you should be able to justify why the rate is a fair reflection of financing costs, credit risk, and administrative time - not a punishment.
• Avoid surprise: Make sure the rate is visible and agreed upfront. Hidden or buried terms are more likely to be disputed.
• Be careful with compounding: Compounding monthly can escalate the cost quickly. That isn’t automatically unlawful, but it needs to be clearly disclosed and defensible.

Separately, many businesses use a fixed late fee (e.g. $15 per reminder) to recover admin time. If you do both (interest plus fees), check that the combined effect is still reasonable.

If your customers are consumers (not businesses), extra care is required. Interest and fees must be clearly disclosed before the sale, fair, and consistent with your obligations under the ACL, including the prohibition on misleading or deceptive conduct. If you trade on standard terms, keep the unfair contract terms regime front of mind - especially for small businesses and consumers.

Daily Rate Example

If your annual rate is 8% p.a. and interest accrues daily on an overdue balance of $1,000, your simple daily rate is 8% / 365 = 0.0219% per day. Daily interest would be $0.219 on day one. Stating the annual rate and accrual method in your contract makes the calculation straightforward.

Should You Charge The Reserve Bank Cash Rate Plus A Margin?

Some businesses peg their late interest to a reference rate (e.g. “RBA cash rate plus 5% per annum”). This can be sensible where interest cycles change. Just define the reference rate clearly and how updates apply.

What If Your Contract Doesn’t Mention Interest?

If you don’t have an agreed late interest clause, you generally can’t unilaterally impose interest after the invoice becomes overdue. You have a few options:

• Offer a variation for future work: Ask customers to accept updated terms (including late interest) before the next job or delivery. Make sure acceptance is clear.
• Negotiate a payment plan that includes interest by consent: For existing overdue amounts, you can propose a repayment schedule that includes a fair interest component. If they agree in writing, you can rely on it.
• Rely on statutory pre‑judgment interest (if you sue): If you commence court proceedings and obtain judgment, a court may award pre‑judgment interest under the relevant court rules. That’s not something you can self‑charge; it’s at the court’s discretion.

Going forward, build late payment terms into your customer contracts. Including clear payment triggers and consequences at the start is far easier than trying to add them later.

Can You Change Terms Mid-Relationship?

You can update standard terms for future orders if you give reasonable notice and obtain acceptance (for example, by requiring re‑acceptance before new work commences or by signature). However, you generally can’t change the rules mid‑engagement for work already done without agreement.

Practical Steps To Reduce Late Payments And Recover Debts

Interest clauses are a useful backstop, but prevention beats cure. These practical steps can make a big difference:

Before You Supply

• Vet customers: For B2B customers, use a credit application that collects trading history, trade references, and the authority to make credit checks.
• Secure your position: For larger credit exposures, consider requiring a personal guarantee, a General Security Agreement, or registering your interest on the PPSR. If you’re new to the PPSR, our overview explains why it matters for small businesses.
• Set clear terms: Make sure your payment terms, late interest, and any fees are front and centre - in your proposal, order form, and agreement.
• Get the paperwork right: If you deliver goods on retention of title terms, ensure your security interest is properly described and registered (timing is critical).

When You Invoice

• Invoice promptly and accurately: Delays and errors cause disputes. Include purchase order numbers if required.
• Offer convenient payment options: Card, bank transfer, and (if suitable) direct debit. If you use direct debit, make sure your authority and processes comply with direct debit laws.
• Use reminders: Automate polite reminders before and after the due date. Attach statements and highlight any interest that will apply (per your agreed terms).

When An Account Becomes Overdue

• Pick up the phone early: Many late payments are oversight or cash flow timing. A quick, friendly call often resolves it.
• Confirm in writing: Follow up with a concise email that references the overdue amount, due date, any agreed interest, and a new deadline.
• Offer a short plan if needed: A two‑ or three‑part payment plan with interest can be better than a stand‑off. Get it in writing and ensure it references your original contract.
• Escalate proportionately: If there’s no response, send a formal letter of demand. If external help is needed, work with a reputable agent or lawyer and keep collection conduct professional (the ACCC/ASIC debt collection guidelines prohibit harassment or coercion).

If your operations rely on regular repeat orders, it’s also sensible to build in suspension or stop‑credit rights for accounts that become seriously overdue. Enforcing those rights early can prevent exposure ballooning.

What Legal Documents Will Help?

Clear, tailored documents are the foundations of getting paid on time - and having leverage if you’re not. Consider the following:

• Terms of Trade: Set out pricing, payment terms, late interest, delivery, risk, warranties, limitations, and your rights if the customer doesn’t pay. These typically apply to all your sales and should be easy to accept (e.g. signature or tick‑box at checkout).
• Credit Application: For B2B accounts, this captures key details, authorises credit checks, and incorporates your trading terms. It can also include director guarantees if appropriate.
• General Security Agreement (GSA): Lets you take a security interest over a customer’s personal property (non‑land assets). You can then register this on the PPSR to improve your priority if the customer becomes insolvent.
• Retention of Title and PPSR Clauses: If you supply goods, ROT clauses say title doesn’t pass until paid. Combined with PPSR registration, they can be powerful protections.
• Collection and Enforcement Provisions: Your contract can require the customer to pay reasonable enforcement costs (subject to fairness requirements). There is also the option of a tailored Debt Collection Agreement with your provider.

If you sell online, pair your trading terms with website checkout terms and a clear payment process. And if you’re considering late fees in addition to interest, make sure both are consistent with your overall approach to late charges under the ACL.

Where Do Interest Terms Live - The Quote, The Contract, Or The Invoice?

Ideally, the interest clause sits in your master agreement or Terms of Trade that the customer accepts before you supply. Your quote can reference those terms (e.g. “This quote is subject to ABC Pty Ltd’s Terms of Trade”). Your invoice can then reiterate payment due dates and point to the already‑agreed interest clause. Relying on an invoice alone is weaker, because it’s often issued after the contract has formed.

Do You Need A Specific Interest Clause For Every Customer?

No. Most small businesses standardise their trading terms so the same rules apply to all customers, with special terms negotiated only where justified. Just ensure your acceptance process is clear for each customer (signature, tick‑box, or purchase order that references your terms).

What About Payment Surcharges Or Card Fees?

Card surcharges are separate from late interest. If you surcharge, keep it to your reasonable cost of acceptance and follow the card scheme rules. Make sure surcharges are disclosed before payment so customers aren’t surprised.

Key Takeaways

• You can charge interest on overdue invoices in Australia if the customer agreed to clear, fair late payment terms before supply.
• Keep your clause specific: due dates, when interest starts, the annual rate, accrual method, any admin fees, suspension rights, and enforcement costs.
• Set a rate you can justify commercially - transparency and proportionality help avoid “penalty” and unfair terms concerns under the ACL.
• If your contracts are silent, you can negotiate interest for a repayment plan by consent, or seek court‑awarded interest if you litigate.
• Prevent late payments with strong onboarding: credit vetting, clear Terms of Trade, a signed Credit Application, and security where appropriate (like a GSA and PPSR registration).
• Automate reminders, keep collection conduct professional, and escalate proportionately. Align your invoicing and payment processes with your legal terms.

If you’d like a consultation on setting up late payment interest and tightening your invoicing and credit terms, you can reach us at 1800 730 617 or team@sprintlaw.com.au for a free, no‑obligations chat.