Deduction Value Calculator NZ 2026

Rates current for the 2026/27 tax year. Reviewed 5 August 2026.

Quick answer A $1,150.00 invoice for something used 100% for business, bought by a GST-registered sole trader with $90,000 of profit, gives a GST claim of $150.00 and an income tax deduction worth $330.00. The true cost is $652.50, not $1,150.00. Every $1.00 of deduction is worth 34.8c to you.
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A deduction reduces the income you are taxed on. It does not hand your money back, and the gap between those two ideas is where a great deal of poor spending happens. Told that something is "a write-off", people hear that it is free, and buy things in March they would never have bought in September. The truth is arithmetic: a deductible purchase costs you the price less your marginal tax rate, so at 33 percent you still pay 67 cents in every dollar. Buying something genuinely needed becomes cheaper; buying something unnecessary still makes you poorer, just slightly less quickly. Two further effects change the number and are routinely conflated. If you are GST registered, the GST comes back through your GST return and the income tax deduction then applies only to the GST-exclusive amount, so claiming the GST-inclusive figure as well would relieve the same money twice. And if the deduction straddles a tax bracket, part of it is relieved at the higher rate and part at the lower, which no single percentage captures. This calculator handles all of it and shows what the purchase actually leaves you out of pocket.

What it really costs you
$652.50
from a $1,150.00 invoice
Total relief
$497.50
GST claim plus tax saved
Each $1 of deduction saves
34.8c
at your marginal rate

Where the relief comes from

Invoice amount$1,150.00
Business use share100%
GST claimed back$150.00
Deductible amount$1,000.00
Tax on profit without the deduction$19,577.50
Tax on profit with the deduction$19,247.50
Income tax saved$330.00
ACC earner levy saved$17.50
Total relief$497.50
True cost to you$652.50
Effective relief rate on the deduction34.75%
Does the deduction cross a bracket?No, all at 33%

What the same expense is worth at other incomes

The identical invoice, relieved against different profits. This is why a deduction is worth more the more you earn.

Annual profitMarginal rateTax savedTrue cost
This is an estimate, not tax advice. Whether an expense is deductible at all, and in what proportion, depends on your circumstances and on the nature of the expense. Entertainment, capital items and mixed-use assets have their own rules and are not modelled here. Confirm your position with Inland Revenue or your accountant.

The March purchase that costs more than it saves

Every year, businesses buy equipment in the final weeks of the tax year specifically to claim it. If the item was going to be bought anyway, bringing it forward is sensible. If it was not, the transaction is straightforwardly loss-making: you part with the full price and recover only your marginal rate of it. At 33 percent, spending $3,000 on something unnecessary saves $990 of tax and destroys $2,010 of capital. The test is simple and worth applying before every such purchase: would I buy this if there were no deduction at all? If the answer is no, the deduction has not changed the answer, it has only made the mistake cheaper.

Why the same receipt is worth different amounts to different people

Because relief happens at the top of your income, not at the average. A person whose profit sits in the 10.5 percent band recovers a tenth of what they spend; one above $180,000 recovers nearly two fifths. The expense is identical, the invoice is identical, and the value differs by almost four times. This also means the value of a deduction changes as your year goes: the same claim is worth more in a strong year than in a weak one, which is occasionally a reason to time discretionary spending, and never a reason to create it.

Worked example

A GST-registered sole trader with $90,000 of profit buys a tool for $1,150.00 including GST, used entirely for business. The GST portion, $150.00, is claimed back through the GST return, leaving a deductible amount of $1,000.00. Tax on $90,000 of profit is $19,577.50; on $89,000 it is $19,247.50. The deduction therefore saves $330.00 of income tax, which is the 33 percent band applying to the whole claim, and a further $17.50 of ACC earner levy, since the levy is charged on the same profit. Total relief is $497.50 and the purchase leaves the business $652.50 out of pocket.

The same invoice against $40,000 of profit would save only $175.00 of income tax, making the true cost $807.50. Nothing about the tool changed. The only variable is the rate the deduction is relieved at, which is set by everything else the business earned that year.

How this is calculated

The deductible amount is the invoice multiplied by the business use share, less the GST portion if you are registered. GST is taken as three twenty-thirds of a GST-inclusive figure, which is the standard way of extracting 15 percent GST from a total. Income tax saved is calculated by working out the tax on your profit and the tax on your profit less the deduction, then taking the difference; this is done rather than applying a single marginal rate so that a deduction spanning two brackets is handled correctly. Rates are those in force from 1 April 2025: 10.5% to $15,600, 17.5% to $53,500, 30% to $78,100, 33% to $180,000, and 39% above that. The ACC earner levy is treated the same way, since it is charged on the same net profit a deduction reduces: the levy at 1.75% is worked out on your profit and again on your profit less the deduction, and the difference is added to the relief. Because the levy stops at the maximum liable earnings of $156,641, a deduction saves no levy above that point unless it brings profit back under it. True cost is the invoice less the GST claim, the tax saved and the levy saved.

Related NZ calculators

Data sources: the rates and thresholds on this page are maintained against Inland Revenue and ACC. Figures are checked twice monthly.

Frequently asked questions

Does claiming an expense mean it costs me nothing?

No, and this is the single most common misunderstanding in self-employment. A deduction reduces your taxable income, it does not refund your money. If you spend $1,000 on a deductible item and your marginal rate is 33 percent, your income tax falls by $330 and your ACC earner levy by a further $17.50, so you are still around $650 out of pocket. Buying something you do not need in order to claim it always leaves you poorer than not buying it. The deduction makes a necessary purchase cheaper; it never makes an unnecessary one free.

How much is a deduction worth in New Zealand?

It is worth the deductible amount multiplied by your marginal tax rate. Because New Zealand rates are progressive, the same expense is worth different amounts to different people: $1,000 saves $105 for someone in the lowest band and $390 for someone above $180,000. This is why a deduction is more valuable the more you earn, and why the same receipt is worth almost four times as much to a high earner as to a low one.

What happens if a deduction takes me into a lower tax bracket?

The deduction is worth more than a single rate suggests, because it comes off the top of your income and can span two bands. If your profit sits just above a bracket boundary, the first part of the deduction is relieved at the higher rate and the remainder at the lower one. The calculator handles this by computing tax with and without the deduction rather than applying one rate, which is the only way to get a bracket-crossing claim right.

Is the GST claim part of the deduction?

No, they are two separate reliefs and confusing them causes double counting. If you are GST registered you claim the GST portion back through your GST return, and the income tax deduction is then based on the GST-exclusive amount only. If you are not registered, there is no GST claim and the deduction is based on the full amount you paid. Claiming the GST and also deducting the GST-inclusive figure would relieve the same money twice.

What if I only use the item partly for business?

Only the business share is deductible, and only that share of the GST is claimable. A laptop used 70 percent for work gives a deduction on 70 percent of its cost. The apportionment must be reasonable and you should be able to explain how you arrived at it, because it is exactly the sort of figure that gets tested if your return is reviewed. Keeping a short record of how the percentage was worked out is worth more than the precision of the number itself.