Understanding the NZ Interest Limitation Rules for Rental Property

Since October 2021, the New Zealand government has been progressively restricting the ability of residential property investors to deduct mortgage interest as an expense against rental income. These interest limitation rules represent one of the most significant changes to property tax in decades, and they affect the vast majority of residential landlords. If you own rental property in New Zealand, or are thinking about investing, understanding these rules is essential for making informed financial decisions.

What Changed and Why

Before 1 October 2021, residential property investors could deduct 100% of their mortgage interest against rental income, just like any other business expense. The government's view was that this created a tax advantage for property investors over first-home buyers, contributing to housing affordability pressures. The solution was to progressively remove the interest deduction for residential rental properties.

The rules apply to 'residential land': broadly, any land with a dwelling on it (or land where a dwelling could be built), excluding certain categories like new builds, emergency housing, and employee accommodation. Importantly, the rules do not apply to commercial property, farmland used in a farming business, or property that qualifies as a new build.

The Phase-Out Timeline

The interest limitation is being phased in over several years. The timeline depends on when you acquired the property and whether it is a new build. For properties acquired before 27 March 2021 (the announcement date), the phase-out works as follows:

• ●1 October 2021 to 31 March 2023: 75% of interest is deductible
• ●1 April 2023 to 31 March 2024: 50% of interest is deductible
• ●1 April 2024 to 31 March 2025: 25% of interest is deductible
• ●From 1 April 2025: 0% of interest is deductible (fully phased out)

For properties acquired on or after 27 March 2021 (that do not qualify as new builds), no interest has been deductible from the date of acquisition. This means if you purchased a residential rental property after March 2021, you have not been able to claim interest at all unless the property qualifies as a new build.

“From 1 April 2025, existing residential property investors who purchased before March 2021 will lose 100% of their interest deduction. For an investor with a $500,000 mortgage at 6.5%, that is approximately $32,500 per year in deductions. Gone. This is not a minor adjustment.”

The New Build Exemption

The major exception to the interest limitation rules is for 'new builds.' A property qualifies as a new build if it received its code compliance certificate (CCC) on or after 27 March 2020. New build status lasts for 20 years from the date the CCC is issued. During that 20-year window, 100% of mortgage interest remains deductible — regardless of when you purchased the property.

This exemption was designed to encourage investment in new housing supply rather than existing housing stock. It has significantly tilted the investment landscape in favour of new builds and off-the-plan purchases. If you are considering a property investment, the new build exemption should be a central factor in your analysis.

• ●New builds with CCC issued on or after 27 March 2020: 100% interest deductible for 20 years
• ●Conversions of non-residential buildings to residential: may qualify as new builds
• ●Subdivisions creating additional dwellings: the new dwelling may qualify
• ●Existing homes with no new CCC: no exemption, standard phase-out applies

How to Calculate the Deductible Amount

For the current income year (ending 31 March 2025), if you acquired your property before 27 March 2021 and it does not qualify as a new build, you can deduct 25% of your interest costs. From 1 April 2025, that drops to 0%. The calculation is based on interest incurred during the income year, apportioned by the relevant percentage.

If you own multiple properties (some new builds and some existing), you need to track the interest for each property separately. Interest on a loan secured against a new build property remains fully deductible, while interest on existing properties follows the phase-out schedule. If you have a single loan secured against multiple properties, you will need to apportion the interest based on the relative values or loan amounts attributable to each property.

Example Calculation

Suppose you own a rental property acquired in 2019 with a mortgage of $600,000 at 6.5% interest. Your annual interest cost is $39,000. For the year ending 31 March 2025, you can deduct 25% of this: $9,750. From 1 April 2025, your deduction drops to $0. Your taxable rental income increases by $39,000, and at a marginal tax rate of 33%, that costs you an additional $12,870 per year in tax compared to full deductibility.

Impact on Cash Flow and Investment Returns

The practical effect of the interest limitation rules is that many rental properties that were previously cash-flow neutral or slightly positive will become significantly cash-flow negative on an after-tax basis. A property that generated a small tax loss (shelter for other income) may now generate substantial taxable income — even if the actual cash position has not changed.

This has led many investors to reassess their portfolios. Some are selling existing properties and reinvesting in new builds to maintain interest deductibility. Others are restructuring their debt to ensure loans are allocated optimally across their portfolio. Some are simply accepting the higher tax cost as part of a long-term capital growth strategy.

What Changed from 1 April 2025

From 1 April 2025, the phase-out is complete for existing properties acquired before 27 March 2021. This is the most impactful year of the transition. Investors who were still deducting 25% of interest in the prior year now deduct nothing. If you have not already adjusted your cash flow forecasts, tax provisioning, and investment strategy for this change, it is urgent that you do so. The tax impact is immediate and significant.

At the same time, the new build exemption continues to provide full deductibility for qualifying properties. If you purchased a new build with a CCC issued after 27 March 2020, nothing changes for you. 100% of your interest remains deductible. This divergence between existing and new-build properties is now at its widest, making the new build classification more valuable than ever.

Planning Strategies

• ●Review your portfolio structure. Ensure loans are allocated to maximise deductibility on new-build properties
• ●Consider selling underperforming existing properties and reinvesting in new builds where interest is fully deductible
• ●Model your after-tax cash flow under the new rules. Many investors are surprised by how much the tax position has changed
• ●If you are purchasing, prioritise properties with new build status (CCC issued after 27 March 2020)
• ●Ensure your accounting records clearly separate interest costs by property to support your tax position
• ●Consider whether your current ownership structure (personal, company, LTC, trust) is still optimal under the new rules