Can NZ Businesses Charge Interest On Overdue Invoices?

Chasing unpaid invoices is one of those parts of running a business that no one puts on the vision board.

You’ve done the work, delivered the goods, or hit the milestone - and then the payment date comes and goes. Suddenly you’re spending your time (and cashflow) following up, sending reminders, and wondering whether you can add interest to encourage quicker payment.

In New Zealand, you can charge interest on overdue invoices in many situations, but the key is doing it properly. The right approach depends on what your customer agreed to, how you communicated your payment terms, and whether the interest rate and wording are fair and enforceable.

Below, we’ll walk through what NZ businesses need to know to charge interest on overdue invoices confidently - and reduce the risk of disputes along the way.

Is It Legal To Charge Interest On Overdue Invoices In New Zealand?

Yes - in many cases, it’s legal for NZ businesses to charge interest on overdue invoices.

The important part is where the right to charge interest comes from. Generally, it will be either:

• Your contract with the customer (for example, your terms and conditions, Terms of Trade, or Service Agreement), or
• A court or tribunal decision awarding interest on a money claim if you take formal recovery action.

In practical terms, if you want to charge late payment interest without a fight, you should aim to have it clearly agreed upfront.

That’s because if you simply add interest to an invoice without any prior agreement, your customer may refuse to pay that portion - and you may end up spending more time and money arguing about enforceability than the interest is worth.

What NZ Law Is Relevant?

This topic usually touches a few key areas of NZ law, including:

• Contract law (your ability to enforce the payment terms the customer agreed to),
• The Fair Trading Act 1986 (making sure your payment and interest terms aren’t misleading and are presented clearly), and
• The unfair contract terms regime (which can apply to certain standard form contracts, including “small trade” contracts, depending on the circumstances).

If you end up having to sue for the debt, there are also specific rules around when a court can award interest on money claims. In many cases, that’s governed by the Interest on Money Claims Act 2016 and the Interest on Money Claims Regulations 2016, which allow interest to be awarded in certain circumstances and at prescribed rates (often from a particular date, such as when the claim is filed, unless the court orders otherwise).

Separately, if a dispute is brought in the Disputes Tribunal, it can sometimes award interest depending on the type of claim and the circumstances - but that’s not something you should rely on as your primary “late payment interest policy”. It’s usually slower and less predictable than having a clear late payment clause from day one.

When Can You Actually Charge Interest (And When Is It Risky)?

Most of the time, the safest and simplest way to charge interest on overdue invoices is to make sure your customer agreed to it before the work started (or at least before they accepted the goods/services).

Here are the most common scenarios.

1) You Have Clear Written Terms Allowing Interest

This is the best-case scenario. Your agreement might be:

• a signed client agreement,
• accepted online terms (for example, “tick to accept” checkout terms),
• Terms of Trade you provided before supplying, or
• terms referenced in a quote that the customer accepted (as long as those terms were actually provided and accessible).

If you already use Terms of Trade or a tailored Service Agreement, late payment interest is often a standard clause - but the wording and rate still need to be reasonable and clearly communicated.

2) Your Invoice Mentions Interest, But Your Contract Doesn’t

This is where things get tricky.

If the only place you mention interest is at the bottom of an invoice (sent after the goods/services were supplied), your customer can argue they never agreed to those terms. An invoice is often treated as a request for payment, not a contract variation.

In other words: putting “2% monthly interest applies to overdue accounts” on your invoice might help as a reminder, but it isn’t always enough on its own to create a legal right to charge that interest.

3) You Want To Add Interest Later As A “Penalty”

If you didn’t agree interest upfront, adding a high interest rate later can look like you’re trying to impose a penalty rather than fairly compensate for late payment.

Under NZ contract law, whether something is an unenforceable “penalty” depends on the substance of the clause and whether it’s out of all proportion to the legitimate interest you’re protecting (for example, the real costs and risks of late payment). If the interest rate is excessive, or the clause is framed in a punitive way, there’s a higher risk it won’t be enforced.

4) Your Customer Is A Consumer (Not A Business)

If you sell to consumers (rather than only to other businesses), you need to be extra careful with how you present payment terms and any interest/fees.

Consumer-facing terms can be more heavily scrutinised, and unclear or unfair clauses can create compliance risk under consumer protection law. If you’re unsure whether your transactions are “consumer” or “trade”, it’s worth getting advice before you roll out a late payment interest policy broadly.

How Do You Set An Interest Rate That’s Enforceable?

Even if it’s legal to charge interest on overdue invoices, the rate and structure matter. The goal is to encourage on-time payment and cover your cost of money - not to “sting” customers.

There’s No One-Size-Fits-All “Legal Rate”

New Zealand doesn’t give all businesses a single default late payment interest rate you can automatically apply to private invoices.

Instead, an enforceable rate usually comes down to:

• what the parties agreed in the contract, and
• whether the term is clearly disclosed and fair in context.

If a dispute ends up in court, the court may award interest under the Interest on Money Claims Act 2016 and Interest on Money Claims Regulations 2016 (or other relevant rules, depending on the type of claim). But that’s different from you unilaterally applying your own invoice interest policy.

Simple Practical Tips For Choosing A Rate

When setting your late payment interest clause, consider:

• Keep it commercially reasonable: very high rates (especially compounding monthly) can attract disputes.
• Be clear about how it’s calculated: daily, monthly, simple interest, compounding interest, etc.
• State when interest starts: for example, “from the day after the due date”.
• Align it with your industry: some industries have common payment practices (like progress payments and retention), which can affect how a clause is perceived.

Also think about whether you want interest to apply automatically, or only after a certain number of days overdue (for example, after 7 or 14 days). A short grace period can help preserve customer relationships while still protecting your cashflow.

Don’t Forget To Check Your Other “Late Payment” Charges

Some businesses include multiple consequences at once, such as:

• late payment interest,
• a fixed admin fee for overdue accounts, and
• recovery costs (like debt collector fees or legal fees).

These can be legitimate, but you should make sure they work together and don’t become excessive overall - otherwise you increase the risk of the clause being challenged as unfair or unreasonable.

How Do You Add Late Payment Interest Properly (Without Spooking Customers)?

If you want to charge interest on overdue invoices and actually recover it, you’ll usually need two things:

• A strong legal foundation (your contract terms), and
• A consistent billing process (so customers can’t say they were surprised by it).

Step 1: Put The Clause In Your Contract Or Trading Terms

For many small businesses, this is done through:

• Business Terms (for standard supply of goods/services),
• Terms of Trade (common for trade, wholesale, ongoing supply), or
• a tailored Service Agreement for project-based or professional services.

It’s important that your contract is actually formed properly - not just sitting on your website or attached to an email no one read. If you’re unsure what makes terms enforceable in the first place, it helps to understand what makes a contract legally binding (offer, acceptance, intention, and clarity around the key terms).

Step 2: Make Sure The Customer Sees The Terms Before They Buy

This sounds obvious, but it’s where many businesses get caught out.

To reduce disputes, build your process so that customers receive (and accept) your terms at a sensible point, such as:

• when you send a quote, include the terms or attach them, and ensure acceptance is documented,
• when customers place an order online, require them to accept the terms at checkout, or
• if it’s an ongoing relationship, have them sign once at onboarding (and make sure updated terms are communicated).

If you’re relying on quotes as part of your contracting process, it’s also worth thinking about when a quote becomes binding - is a quotation legally binding often comes down to the wording and the acceptance process.

Step 3: Reflect The Clause On Your Invoices (As A Reminder)

Even if your legal right comes from the contract, it’s still helpful to repeat the key payment information on each invoice, including:

• the due date,
• your interest rate (or a short reference to the clause), and
• what happens if the invoice isn’t paid on time (for example, suspension of services, recovery costs).

The invoice reminder won’t fix missing contract terms - but it can support your position and reduce “I didn’t know” pushback.

Step 4: Apply It Consistently (Or Have A Clear Policy When You Won’t)

If you only charge interest sometimes, customers may argue you’ve waived your rights or that the term isn’t really part of the bargain.

That doesn’t mean you can’t make commercial calls (for example, waiving interest for a long-term client once as a goodwill gesture). Just make sure your team knows:

• when interest applies automatically,
• who can approve a waiver, and
• how to document that waiver in writing.

What If The Invoice Is Still Unpaid - Can You Enforce The Interest And Recover The Debt?

Sometimes the bigger issue isn’t the interest - it’s the underlying debt.

If an invoice is overdue, you’ll usually want to move through a clear escalation pathway. A typical approach looks like this:

1) Send A Friendly Reminder (Immediately After The Due Date)

Keep it short and polite. In a lot of cases, late payment is just admin delay.

2) Send A Formal Overdue Notice

If payment doesn’t come through, send a firmer email/letter that:

• confirms the invoice is overdue,
• references the interest clause in your terms, and
• sets a deadline for payment before next steps.

At this stage, you can also flag any other contractual consequences (like pausing further work).

3) Consider A Letter Of Demand

A letter of demand can be a strong “line in the sand” before you take legal action. It also shows you’re taking the debt seriously and creates a paper trail.

4) Escalate To Debt Recovery Or Legal Action

If you need outside help, you may consider engaging a debt collector or lawyer. If your contract allows you to recover reasonable costs of enforcement, this can sometimes be added to the debt (again, it needs to be properly drafted and reasonable).

Can You Claim Interest If You End Up In Court Or The Disputes Tribunal?

Potentially, yes. If you bring a claim for an unpaid invoice, interest might be awarded depending on:

• what your contract says (if you have a late payment interest clause), and/or
• the rules that apply to awarding interest on money claims through the relevant forum (including, in many cases, the Interest on Money Claims Act 2016 and Interest on Money Claims Regulations 2016).

That said, relying on “we’ll sort it out in court” is rarely ideal for a small business. It takes time, costs money, and can damage customer relationships.

The more effective strategy is usually to build your interest clause and payment enforcement process into your business systems from day one - so you don’t have to improvise when cashflow gets tight.

Key Takeaways

• In many situations, it is legal for NZ businesses to charge interest on overdue invoices, but it’s safest when the customer agreed to it upfront in your contract terms.
• If the only mention of interest is on your invoice (sent after supply), it can be harder to enforce because the customer may argue they never accepted that term.
• Late payment interest rates should be commercially reasonable, clearly explained (including how and when interest is calculated), and consistent with how you actually run your invoicing process.
• Present your payment terms clearly before the customer buys - for example, in your Terms of Trade, Business Terms, or a tailored Service Agreement.
• If an invoice remains unpaid, follow a clear escalation pathway (reminders, overdue notice, letter of demand, then debt recovery/legal action if needed).
• Courts (and, in some cases, the Disputes Tribunal) may be able to award interest on money claims under specific legal rules, including the Interest on Money Claims Act 2016 and Interest on Money Claims Regulations 2016 - but it’s usually better to rely on clear contract terms than hope interest is added later through the process.
• Getting the legal foundations right early can save you a lot of time, stress, and cashflow risk later - especially as your customer base grows.

If you’d like help putting enforceable late payment interest clauses into your terms (or you’re dealing with a tricky overdue invoice dispute right now), you can reach us at 0800 002 184 or team@sprintlaw.co.nz for a free, no-obligations chat.