Tax Debt in New Zealand — Interest, Penalties and Options

Tax Debt in New Zealand — Interest, Penalties and Options

Owing Inland Revenue is uncomfortable in a way that has less to do with the size of the debt than with the fact that it doesn't go away. The amount is fixed, the clock starts, and interest is charged for using money that should already have been paid.

That is the right way to read it. Use-of-money interest is not a punishment added on top of a debt; it is a charge for holding money that was due. The distinction matters, because it changes what a sensible response looks like.

This guide sets out how the interest is worked out, how the rates have moved, and what genuinely reduces the cost of a debt.

How We Researched This Guide

The rates and rules here are taken from Inland Revenue's own guidance on interest on overpayments and underpayments, together with its published provisional tax material. These rates are set by reference to market rates rather than fixed for good, so the current figures are the only ones worth quoting.

Two characteristics are worth noticing before anything else. The interest is calculated daily and does not compound, and it is not included when penalties are calculated. Both make the arithmetic more predictable than a compounding debt would be — which is precisely why delay, rather than the size of the amount, is what drives the total cost.

The Quick Summary (60-Second Version)

What you need to know before the detail.

• Interest is a charge for the use of money, not a penalty.
• From 16 January 2026, the underpayment rate is 8.97 per cent per year, and the overpayment rate is 2.25 per cent per year.
• Interest is calculated daily, does not compound, and is not included when penalties are calculated.
• Interest starts the day after the original due date for the amount owing.
• Payments to clear unpaid tax go first to unpaid interest, then to tax, except for provisional tax paid as directed.
• Interest you pay is deductible where it relates to business purposes, and interest paid to you is gross income.

Why Interest Is Not a Penalty

The label matters because of what it implies about the fix. A penalty is imposed for doing something wrong, and you can't discuss the amount. A use-of-money charge reflects the fact that tax due in, say, April has been available to you rather than to the Crown since then.

Because the charge is for the time the money was held, the lever available to you is time. Paying sooner reduces it and paying later increases it. The rate is anchored to what money costs in the market rather than set as a deterrent.

That is also why the mechanism is designed to work in both directions. Inland Revenue pays interest on overpayments at the overpayment rate, so the system is symmetrical in principle even though the two rates are very different in size.

How the Rates Are Set, and How They Have Moved

The underpayment rate is built from the Reserve Bank's floating first mortgage new customer housing rate plus 250 basis points — 2.5 per cent on top. The overpayment rate uses the Reserve Bank's 90-day bank bill rate less 100 basis points, with a floor of 0 per cent so that an overpayment never accrues negative interest.

Because both are anchored to market rates, they move with those rates. The current settings have been in force since 16 January 2026.

The gap between the two columns is the honest story in that table. Charging considerably more than the rate paid on an overpayment makes a debt expensive to carry and a credit balance barely worth holding. That is a deliberate design choice, not an arithmetic accident.

The direction of travel is also worth noting. Each set of rates in the table is lower than the one before it, so the cost of carrying a debt has fallen without anyone having to do anything about it.

Why the Arithmetic of Delay Is the Real Problem

Interest is calculated daily and does not compound. That makes it linear. The same daily charge applies whether the debt is one day old or one year old, so the total grows steadily rather than accelerating.

Linear is not harmless. A steady daily charge on a fixed amount still produces a total that grows with every week of delay, and because nothing about the debt changes on its own, payment is the only thing that stops the growth.

What makes delay worse than the arithmetic alone suggests is how it interacts with new obligations. Unpaid tax doesn't pause the rest of the system, so an older debt can sit alongside new liabilities as they arise, with interest running on the older amount throughout.

Interest starts the day after the original due date for the amount owing. The calculation includes no grace period, so the date matters more than the amount in the early weeks.

How Payments Are Applied, and What Can Be Deducted

When you pay money against unpaid tax, it applies to unpaid interest first, then to tax. That ordering matters, because it means the interest balance clears before the principal starts reducing.

There is one exception worth knowing. Provisional tax payments are applied to instalments as the taxpayer directs, rather than being swept into the interest-first ordering. If you have a mix of provisional obligations and older debt, that difference changes how a payment takes effect.

On deductibility, interest you pay on an underpayment is deductible for business purposes and can be claimed as an expense. Interest paid to you on an overpayment works the opposite way: it is gross income and must be included on your return in the year you receive it, even if you use it to pay other unpaid tax.

Those two rules are often overlooked in opposite directions — one relieves a cost, and the other creates an obligation that is easy to forget once the money has already been spent.

The Options That Actually Reduce the Cost

Reducing the cost of a tax debt comes down to a few things, none of them complicated.

First, pay sooner rather than later. Because the charge is daily and does not compound, every day of delay adds a fixed increment, and every payment reduces the balance that the increment is charged on. There is no advantage in waiting for a better moment.

The second is understanding the order in which payments are applied. Because interest is applied before tax, an older balance with accrued interest absorbs a payment differently from a fresh one, and the older balance usually costs more per dollar owed.

The third is claiming what you can claim. If the interest relates to business purposes, you can deduct it as an expense, reducing the net cost of the debt even though it does not reduce the debt itself.

The fourth doesn't add to it. A tax debt does not pause other obligations, and interest continues to run on the older amount regardless of what has arisen since. Keeping current obligations current is what stops one balance from becoming two.

Keep in mind a small tolerance in the provisional tax context. Inland Revenue does not charge or pay interest where you underpay or overpay by $100 or less. It is a rounding allowance rather than a strategy, but it means very small differences aren't worth chasing.

Questions You Might Have

Does the interest compound?

No. It is calculated daily and does not compound, so the charge grows steadily rather than accelerating. The rate has also stepped down with market rates rather than drifting upwards.

Is interest included when penalties are calculated?

No. Interest is not included when penalties are calculated, which keeps the two separate: a penalty is assessed on the underlying position, while interest is charged for the time the money was held.

Why is the underpayment rate so much higher than the overpayment rate?

They use different benchmarks and margins. The underpayment rate adds 250 basis points to the Reserve Bank's floating first mortgage new customer housing rate, while the overpayment rate subtracts 100 basis points from the 90-day bank bill rate, with a floor of 0 per cent.

Can I deduct the interest I have been charged?

Where it relates to business purposes, yes. Interest you pay on an underpayment is deductible and can be claimed as an expense. Interest paid to you on an overpayment is gross income and belongs in your return in the year it was refunded.

If Inland Revenue pays me interest, is it taxed?

Yes. Interest paid to you on an overpayment is gross income and must be included in your return in the year it was refunded, even if you used it to settle other unpaid tax.

What Matters Most

A tax debt is better treated as a cost of time than as a judgment. Interest is charged for holding money that was due; it runs daily and does not compound, so the total is predictable, and the response is straightforward.

The arithmetic of delay is the real problem. Every week without a payment adds another increment, and the charge runs on the older balance even as new obligations appear alongside it. Waiting doesn't improve that dynamic.

All rates and rules here are taken from Inland Revenue's published material. Where a figure could not be confirmed against it, it does not appear.