Provisional tax is income tax paid in instalments during the year, and it's the single most common cash-flow surprise for New Zealand businesses. Here's who pays it, how it's calculated, when it's due, and how to keep it from biting.
What provisional tax actually is
Provisional tax is not a separate tax. It's just income tax paid in advance, in instalments, during the year it relates to, instead of in one lump sum after year-end. Think of it as pre-paying your tax bill in chunks as you earn, the same way PAYE quietly takes tax from a salary each payday.
The logic is simple. If you owed a meaningful amount of tax last year and your income is likely to be similar this year, IRD asks you to pay towards this year as you go, rather than letting a large bill build up to be settled all at once. At the end of the year your actual tax is worked out, the provisional instalments you paid are credited against it, and you either have a small balance to pay or a refund.
For someone used to a salaried job where tax "just happens", this is the big mental shift of self-employment: no tax comes out of your invoices automatically, so provisional tax is the system that spreads the load. Understood ahead of time, it's manageable. Discovered the hard way, it's the classic first-year shock.
Who has to pay it (the $5,000 rule)
You become a provisional taxpayer once your residual income tax (RIT) for a year is more than $5,000. Residual income tax is, broadly, the tax left owing on your income for the year after any tax already deducted at source (like PAYE or withholding on schedular payments) is taken off.
| Last year's residual income tax | This year |
|---|---|
| $5,000 or less | No provisional tax required |
| More than $5,000 | You pay provisional tax in instalments toward the next year |
So in your first profitable year you might simply pay your tax bill once. But if that bill exceeds $5,000, you tip into provisional tax for the following year. This is exactly why the second year so often feels heavier: you can be settling year one and paying the first provisional instalments toward year two close together.
The $5,000 line applies to individuals, sole traders, and companies alike. If you're hovering near it, it's worth knowing in advance, because crossing it changes how and when you pay. Our guide to residual income tax explains the figure in more detail.
Standard, estimation and AIM methods
There are several ways to work out your provisional tax, and the right choice depends on how predictable your income is.
| Method | How it's calculated | Suits |
|---|---|---|
| Standard (uplift) | Last year's RIT plus a set uplift percentage | Steady or modestly growing income |
| Estimation | You estimate this year's RIT and pay on that | Income that's clearly falling |
| AIM | Calculated from actual profit each period via accounting software | Variable income, newer businesses |
| Ratio | Based on your GST taxable supplies | GST-registered, eligible turnover |
The standard method is the default and the simplest: it assumes this year resembles last year, with an uplift. The estimation method lets you pay less if your income is genuinely dropping, but if you under-estimate you'll wear use-of-money interest on the shortfall. AIM is the standout for variable or new businesses, because you only pay tax when your software shows you've actually made a profit that period, so you never pay on income you haven't earned yet. We help clients pick the method that smooths cash flow and minimises interest, and set it up properly.
Instalment dates
Most provisional taxpayers on the standard method pay in three instalments across the year, typically falling in August, January, and May for a standard 31 March balance date. If you're also GST-registered and file six-monthly, your provisional tax may align to that cycle.
The exact dates depend on your balance date (your financial year-end) and your method. AIM works differently again, with payments made more frequently through the year as your software calculates them, which is part of why it tracks real income so closely.
- Standard method: three instalments, spread across the year
- Six-monthly GST filers: two instalments aligned to GST
- AIM: payments at each GST/AIM period, based on actual profit
The practical point is that these are fixed dates you can diarise. Once you know them, provisional tax stops being a surprise and becomes a budget line. We give every client a clear payment schedule for the year so nothing arrives unexpectedly. This is general information; your exact dates depend on your balance date, so confirm with us or check ird.govt.nz.
Use-of-money interest and safe harbour
If you pay too little provisional tax during the year, IRD charges use-of-money interest (UOMI) on the shortfall, effectively interest on tax you should have paid sooner. On a sizeable bill at the applicable rate, it adds up.
Your main shield is the safe-harbour rule. In broad terms, if you pay your standard provisional instalments in full and on time, you're generally protected from UOMI until the final balance date, even if your actual tax turns out higher than the standard calculation. That's a powerful certainty: it converts an unpredictable interest risk into a set of known payments.
- Pay standard instalments on time and on the prescribed amounts, and you're usually inside the safe harbour.
- Estimate too low, or miss an instalment, and interest can apply from earlier in the year.
- Tax pooling is a further option to manage UOMI on a shortfall, letting you effectively buy tax dated to the right period.
We make sure clients use safe harbour where it helps and reach for tax pooling when a one-off income spike would otherwise create interest. Our provisional tax safe harbour guide covers it fully.
How to avoid a surprise bill
The whole problem with provisional tax is timing, not the tax itself, and timing is controllable. A few habits keep it tame:
- Set money aside as you invoice. Many sole traders move a sensible slice of every payment into a separate tax account so the cash is there when instalments fall due.
- Know your dates. Diarise the instalments at the start of the year so none of them ambushes you.
- Choose the right method. If income is lumpy or new, AIM means you pay on real profit, which avoids overpaying.
- Plan for the second-year overlap. If this is your first big year, expect the year-one bill and the first year-two instalments to land close together, and save for both.
- Review if income changes. A sharp drop may justify estimating down; a jump may warrant a top-up to stay inside safe harbour.
None of this is complicated, it just needs doing before the bill arrives rather than after. That's exactly what we set up with clients: the right method, a clear schedule, and a savings habit that matches it.
This page is general information only, not personalised tax advice. Your situation may differ, so book a free review to talk it through. In plain English: provisional tax is just your income tax paid in instalments, so once you know your method and dates and set money aside as you earn, it stops being a surprise.
This is general information, not personalised tax advice.See our full disclaimer.