How To Charge And Recover Late Payment Interest In New Zealand

Late invoices are one of the fastest ways to turn a “good month” into a stressful one.

If you’re a small business owner, you’ve probably had at least one customer who pays late (or only pays after reminders). And while you might feel awkward chasing, the reality is that cashflow is your business’s oxygen.

Charging late payment interest can be a practical way to:

• encourage customers to pay on time;
• compensate you for the cost of waiting; and
• set clear boundaries about how your business operates.

But there’s a catch: you can’t usually just add interest after the fact because you’re frustrated. To charge late payment interest (and actually recover it), you need to set it up properly in your contract documents and invoicing process.

Below, we’ll break down how late payment interest works in New Zealand, what you need in your terms, how to calculate it, and what to do if the invoice is still unpaid.

What Is Late Payment Interest (And When Can You Charge It)?

Late payment interest is an amount you charge a customer when they pay an invoice after the due date. It’s usually expressed as a percentage rate (for example, “1.5% per month”) and often accrues daily or monthly until the debt is paid.

For most small businesses, the key point is:

It’s best to have a clear contractual right to charge late payment interest.

That right usually comes from:

• your terms and conditions (sometimes called “terms of trade”);
• a signed service agreement or customer contract; and/or
• a credit application that the customer signs and agrees to.

If you don’t have that right clearly written into your agreement, adding interest later can be much harder to enforce (especially if the customer disputes it). In some cases, even without a specific contract term, interest may still be available through court processes or statutory powers if you end up taking formal action - but relying on that is usually slower, more expensive, and less predictable than having a clear clause upfront.

Late payment interest is most commonly used in B2B arrangements (for example, suppliers, trades, professional services, agencies), but it can also apply in some B2C situations. If you sell to consumers, you’ll want to be particularly careful that your terms are transparent and not unfair or misleading.

Is Late Payment Interest The Same As A Late Fee?

Not quite.

• Late payment interest is typically calculated as a percentage that accrues over time.
• Late fees are often a fixed amount charged once (for example, “$30 if payment is more than 7 days overdue”).

Both can be lawful, but both should be clearly set out in your contract documents upfront. If you’re using fixed fees, you’ll also want to make sure they’re defensible as a genuine estimate of the costs of late payment (rather than a “penalty”). In practice, whether something is an unenforceable penalty depends on how the clause operates and whether it’s out of proportion to the legitimate costs or interests you’re protecting - so it’s worth getting the wording right.

How Do You Set Up Late Payment Interest So It’s Enforceable?

If you want to actually recover late payment interest, your best friend is a well-drafted contract or set of business terms.

In practice, you’re aiming for two things:

• Clear agreement: the customer agreed to the term before you supplied the goods/services.
• Clear wording: the interest clause is specific enough that it’s easy to calculate and hard to argue about.

Many businesses rely on Business Terms (or terms of trade) that apply to every job, plus a quote or proposal that references those terms.

What Should Your Late Payment Interest Clause Include?

A solid late payment interest clause usually covers:

• When interest starts (e.g. the day after the due date).
• The interest rate (e.g. “X% per month” or “X% per annum”).
• How it accrues (daily, monthly, compounding or simple interest).
• Whether interest applies to the full outstanding amount (including GST, costs, and any prior fees).
• Your right to recover debt collection / enforcement costs (this often matters just as much as the interest).

It also helps if your clause makes it clear that charging interest doesn’t limit your other rights (for example, pausing work, suspending access, or starting debt recovery).

Where Should The Customer Agree To It?

For small businesses, the most common “agreement points” are:

• a signed service agreement (for ongoing or higher-value work);
• an accepted quote that incorporates your terms;
• online checkout terms (for ecommerce);
• a signed credit application (especially for trade accounts);
• a master agreement plus statements of work for repeat projects.

If you provide services on an ongoing basis, it can also be worth putting your terms into a tailored Service Agreement so the payment, invoicing and interest rules are all in one place.

One common mistake is relying on “terms on the back of the invoice”. By the time the invoice is issued, the goods/services have usually already been supplied - so you’re asking the customer to accept new terms after the event, which is risky if it ends up in a dispute.

What Interest Rate Can You Charge In New Zealand?

There isn’t one single “official” late payment interest rate that automatically applies to every business invoice in New Zealand.

Instead, what you can charge often comes down to what you and the customer agreed to in your contract, and whether the clause is reasonable and properly disclosed. If you end up in a dispute or formal recovery process, a court (or tribunal) may also have the power to award interest in certain circumstances - but that’s different to having an agreed contractual rate you can apply through your normal invoicing process.

As a practical guide, businesses often choose an interest rate that:

• is high enough to discourage late payment;
• is not so high that it looks punitive;
• is clearly explainable and easy to calculate; and
• fits the industry norm for your sector.

If you’re contracting with consumers, you should be extra cautious. You don’t want to create terms that could be challenged as unfair, or run into issues under the Fair Trading Act 1986 (for example, if the term is not disclosed clearly) or under unfair contract terms rules that can apply to standard form consumer (and, in some cases, small trade) contracts. The safest approach is to keep the term prominent, easy to understand, and proportionate to your legitimate interests.

Should You Use “Per Month” Or “Per Annum”?

Either can work, but you should be consistent and crystal clear.

• “1.5% per month” is easy to understand but people sometimes misread it.
• “18% per annum calculated daily” is often clearer for calculation purposes (and it’s the same rate as 1.5% per month in simple terms).

Whichever you choose, your clause should say how it’s calculated (daily/monthly) so there’s no argument later.

How Do You Calculate Late Payment Interest (And Show It On An Invoice)?

Even if you have a solid clause, you still need a process that’s easy to apply. If it’s complicated, many businesses don’t enforce it consistently - and inconsistency can undermine your position in a dispute.

A Simple Calculation Approach

Here’s a common method used in commercial terms:

• interest rate is expressed per annum;
• interest accrues daily on the overdue amount;
• the interest amount is added to the next invoice or statement.

A basic formula (simple interest) looks like:

Interest = Overdue Amount × Annual Interest Rate × (Days Overdue ÷ 365)

For example (illustrative only): if $10,000 is overdue, your agreed interest rate is 18% per annum, and the invoice is 30 days late:

• $10,000 × 0.18 × (30 ÷ 365) ≈ $147.95

You can then invoice that interest amount (or include it on the customer’s statement as “late payment interest”).

How To Communicate Interest Without Escalating The Relationship

A lot of business owners hesitate because they don’t want to damage customer relationships. That’s fair - but a professional, consistent approach usually helps.

Some practical tips:

• Reference the contract term in reminders (“As per our terms, interest may apply to overdue amounts”).
• Warn before applying it (“If payment isn’t received within 7 days, we’ll apply late payment interest”).
• Apply it consistently (or at least have a policy for when you do).
• Keep the tone neutral - treat it like an admin step, not a personal dispute.

And if you want to preserve goodwill, you can always waive the interest once payment is made - the important part is that you have the right to charge it and can use it when needed.

What If The Customer Still Doesn’t Pay?

Late payment interest is helpful, but it won’t magically make a non-paying customer pay. If the invoice remains outstanding, you’ll generally move through an escalation pathway.

A sensible step-by-step approach often looks like this.

1) Check Your Paperwork First

Before you go harder on recovery, check:

• Did the customer actually agree to your terms?
• Do your terms clearly allow late payment interest and debt recovery costs?
• Is the invoice accurate (right entity name, right amount, right due date)?
• Do you have evidence the goods/services were delivered or performed?

If you’re relying on a quote and acceptance process, it’s worth tightening this up for future jobs so you’re protected from day one.

2) Send A Clear Overdue Notice

Your reminder should be short, factual and dated. Include:

• the invoice number and original due date;
• the outstanding amount;
• how to pay;
• a payment deadline; and
• a note that late payment interest and recovery costs may apply under your terms.

If you supply ongoing services, you may also want to consider whether you have the contractual right to suspend services for non-payment (and if you do, whether it’s commercially sensible in the situation).

3) Consider A Formal Letter Of Demand

If reminders aren’t working, the next step is often a letter of demand. This is where you clearly state:

• the amount owed (including any interest claimed under your contract);
• the deadline to pay;
• what you’ll do if payment isn’t made (for example, debt collection or legal proceedings).

This step can be particularly effective when you’re dealing with a customer who is delaying payment because they don’t think you’ll follow up.

4) Debt Collection, Disputes, Or Legal Action

If the invoice is still unpaid, your next steps depend on the size of the debt, whether the customer is disputing it, and how strong your documentation is.

Options can include:

• negotiating a payment plan (and documenting it);
• using a debt collection agency;
• taking action through the Disputes Tribunal (where appropriate);
• court proceedings for higher value or more complex matters.

This is also where having properly drafted terms can make a real difference - especially terms that cover interest and recovery costs, and are incorporated into the deal correctly.

How Do You Avoid Late Payment Problems In The First Place?

It’s much easier (and cheaper) to prevent late payments than to chase them.

Here are some practical legal and commercial steps that help reduce the risk.

Use Proper Contracts And Strong Payment Terms

If you’re doing project-based work or ongoing services, set out payment terms clearly upfront - including when invoices are due and what happens if they’re not paid.

Depending on your business model, you might use:

• Service Agreement terms with clear invoicing and consequences for non-payment;
• Master Services Agreement arrangements for repeat work;
• Terms Of Trade if you supply goods or provide services across lots of customers.

Good terms don’t just help you charge late payment interest - they also help you prove what was agreed if a customer tries to dispute the invoice later.

Be Careful With Verbal Arrangements

Verbal agreements can be enforceable in New Zealand, but they’re harder to prove (and disputes about payment terms are common).

Even a simple written acceptance of a quote and a link to your terms can save you a lot of time later.

Consider Deposits, Progress Payments, Or Payment Upfront

If cashflow is critical (or you’ve been burned before), structure your pricing so you’re not carrying the full risk of non-payment.

For example:

• a deposit before work begins;
• milestone/progress payments;
• shorter invoice terms (e.g. 7 days instead of 30).

This is a commercial decision - but it’s also something you can bake into your contract terms so there’s no confusion.

Make Sure Your Contracting Entity Is Correct

This one is easy to overlook. If you’re contracting with “John Smith” but the business is really “Smith Holdings Limited”, you might have trouble enforcing payment against the right party.

Good onboarding processes (and well-drafted terms) reduce this risk.

Protect Your Business Systems And Data As You Grow

Late payment issues often come with more admin: follow-ups, storing customer details, escalating disputes, and sometimes sharing information with advisors.

If you collect customer information (especially online), make sure you’ve got the right privacy settings and documents in place, like a Privacy Policy, so your debt recovery processes don’t create new compliance headaches.

Key Takeaways

• Late payment interest is most enforceable when your customer agreed to it upfront in your contract terms or service agreement (and it’s clearly incorporated into the deal).
• Your interest clause should clearly state when interest starts, the rate, and how it’s calculated (daily/monthly and whether it compounds).
• Adding interest for the first time on an invoice (after the work is done) is risky - it’s better to incorporate your terms before you supply goods or services.
• Choose an interest rate that’s commercially reasonable and transparent, especially if you deal with consumers.
• Have a consistent process: reminders, overdue notices, and (if needed) a letter of demand or formal debt recovery steps.
• Strong contracts and business terms don’t just help you claim interest - they also help you recover debt collection costs and reduce disputes about what was agreed.

If you’d like help setting up payment terms that actually work in practice (including late payment interest clauses that fit your business), we can help. Get in touch at 0800 002 184 or team@sprintlaw.co.nz for a free, no-obligations chat.