This New Zealand calculator is built for people earning extra income alongside a main job, from freelancing and selling online to driving or renting a room. It estimates the additional income tax on that side income at your top marginal rate, flags when your total income may push you into provisional tax territory, and shows roughly how much you should set aside from each payment so there is no nasty bill at year end. It also helps you account for deductible expenses against the side income, so you are taxed on profit rather than turnover. The breakdown separates the tax, the suggested savings buffer, and your take-home from the side hustle, giving a realistic picture of what the extra effort actually leaves in your pocket and helping you stay on the right side of Inland Revenue.
Estimate only, based on the 2025/2026 tax year and income tax brackets. It does not include ACC levies or GST, which may also apply to self-employed income. Rates and thresholds change, so check the current figures. This is general information, not tax advice.
Your side income sits on top of your main income, so it is taxed at your marginal rate, the rate that applies to your highest dollars. The calculator first works out your profit by taking your side income and subtracting deductible expenses, because you are taxed on profit, not turnover. It then compares the income tax on your total income with the tax on your main income alone, and the difference is the tax on your side hustle. The set-aside percentage is that tax as a share of your side profit, which is how much of each payment to reserve.
On a $70,000 main income with $12,000 of side income and $2,000 of expenses, the side profit is $10,000. Sitting on top of $70,000, most of that profit is taxed at 30%, so the extra tax is around $3,000, meaning you should set aside roughly 30% of what you earn from the side hustle.
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