First-Year Provisional Tax Safe-Harbour Calculator
First year of self-employment? You don't pay provisional instalments during the year — the full RIT falls due as terminal tax. This calculator checks whether you're inside IRD's $60,000 safe harbour and previews next year's instalment schedule.
Self-employed profit after expenses, plus any other taxable income.
If you also had a PAYE day job, RWT on interest, or imputation credits, enter the total withheld.
How first-year provisional tax works
The standard provisional method calculates instalments as 105% of last year's RIT, split across three dates. In your first year of self-employment there's no prior-year RIT to multiply, so no instalments are required — but the full first-year tax balance is owed in one hit on terminal tax day.
IRD's $60,000 safe harbour (Income Tax Act 2007 s RC 12) protects first-year filers from UOMI as long as RIT stays under the threshold and the balance is paid on time. Above $60k, IRD treats you as if you should have been paying instalments and back-charges UOMI from each missed date.
From year 2 onwards, you enter the standard provisional regime with three instalments (28 August, 15 January, 7 May for a 31-March balance date). The base for the calculation is your year-1 RIT × 105%.
Frequently asked questions
Do I have to pay provisional tax in my first year of self-employment?
No. Standard provisional uses 105% of prior-year RIT — and your prior year RIT is zero. The full RIT is owed as terminal tax. Optional voluntary instalments are available via the estimation method if you want to spread the cash flow.
What counts as RIT?
Residual income tax = income tax owed for the year minus PAYE / RWT / imputation credits already withheld. For pure self-employed with no PAYE day-job, RIT roughly equals the income tax on your business profit.
What happens if I'm above the $60k safe-harbour threshold?
You don't lose the right to pay at terminal tax time — but UOMI applies from when the standard instalments would have been due (28 Aug, 15 Jan, 7 May) up to the date you eventually pay. The rate is around 10.91% p.a. simple daily, so the longer the gap, the worse the bill.
Can I use the estimation method instead?
Yes. The estimation method lets you forecast your own current-year RIT and pay one-third at each provisional date. Used well, it caps UOMI exposure. Under-estimate and UOMI applies from each missed instalment — so estimate generously, not aggressively.
What changes in year 2?
You move onto standard uplift: instalments are 105% of year-1 RIT (110% if only year-before-last is filed), split equally across 28 Aug, 15 Jan, and 7 May. The terminal tax wash-up runs the following 7 Feb. Plan cash flow now — that's three instalments due in your second 12 months, on top of any second-year terminal tax.
Related calculators
Sources
Safe-harbour rules from IRD — Safe-harbour rules and IRD — Provisional tax. UOMI rate from IRD — Use of money interest.