The Rental Interest Deductibility Calculator helps New Zealand residential landlords work out how much of the interest on their rental loan they can claim against rental income, and the tax that claim saves. Interest deductibility on residential rental property was wound back and then restored over several years, so the percentage you can deduct depends on the income year. For the year to 31 March 2024 only 50 percent of interest was deductible, for the year to 31 March 2025 the rate is 80 percent, and from 1 April 2025 onwards interest is once again fully deductible at 100 percent. You enter the total interest paid on your residential rental loan for the year, choose the income year, and pick your marginal tax rate, and the tool returns the deductible interest along with the approximate tax effect of that deduction. Landlords, accountants, and property investors use it to estimate the deduction before filing an IR3 or company return and to compare how the changing rules affect cash flow across years. A few good habits help here. Keep your interest figure separate from principal repayments, because only interest is ever deductible, and make sure the loan genuinely relates to the rental rather than private borrowing. Match your marginal rate to your total taxable income, since a higher rate makes each dollar of deduction worth more. Finally, remember that new builds and some other property may follow different rules, so confirm your situation with your accountant. This calculator gives a clear estimate to plan with, not formal tax advice, but it makes the phase back easy to understand at a glance.
Deductible interest = interest x year percentage. Tax saving = deductible interest x marginal rate. Estimate only, not financial or tax advice.
The tool multiplies your interest by the deductibility percentage for the chosen income year, which is 80 percent for the year to 31 March 2025. It then multiplies that deductible interest by your marginal tax rate to estimate the tax saved. Only interest is deductible, never principal.
With $20,000 of interest in the year to 31 March 2025, the deductible share is 80 percent, giving $16,000 of deductible interest. At a 33 percent marginal rate the deduction saves about $16,000 times 0.33, which is $5,280.
If you've found a bug, or would like to contact us, or learn more about James Graham and Calculate.co.nz.
Calculate.co.nz is partnered with Interest.co.nz for New Zealand's highest quality calculators and financial analysis.
All calculators and tools are provided for educational and indicative purposes only and do not constitute financial advice.
Calculate.co.nz is proudly part of the Realtor.co.nz group, New Zealand's leading property transaction literacy platform, helping Kiwis understand the home buying and selling process from start to finish. Whether you're a first home buyer navigating your first property purchase, an investor evaluating your next acquisition, or a homeowner planning to sell, Realtor.co.nz provides clear, independent, and trustworthy guidance on every step of the New Zealand property transaction journey.
Calculate.co.nz is also partnered with Health Based Building and Premium Homes to promote informed choices that lead to better long-term outcomes for Kiwi households.
Calculate.co.nz is hosted in Auckland via SiteHost new Zealand.
All content on this website, including calculators, tools, source code, and design, is protected under the Copyright Act 1994 (New Zealand). No part of this site may be reproduced, copied, distributed, stored, or used in any form without prior written permission from the owner.
© 2019 to 2026 Calculate.co.nz. All rights reserved.