How does the planner work it out?
GST. New Zealand GST is 15%, so GST is 3/23 of any GST-inclusive amount. The planner takes 3/23 of your sales, subtracts 3/23 of your claimable expenses, and divides the result by the number of weeks in your filing period — about 4.3 for monthly, 8.7 for two-monthly and 26 for six-monthly.
Provisional tax. Under the standard option, this year's provisional tax is generally last year's residual income tax (RIT) plus 5%. You're a provisional taxpayer if your RIT was more than $5,000. For a 31 March balance date, instalments are due on 28 August, 15 January and 7 May — or 28 October and 7 May if you file GST six-monthly. The planner spreads the annual amount over 52 weeks so the money is there when each instalment arrives.
Why a weekly set-aside works
GST and provisional tax are the two bills most likely to push a healthy small business into IRD debt. The money comes in with every sale, but the bill arrives weeks or months later — by which time it's often been spent on wages or stock. Moving a fixed amount into a separate tax account every week turns a lump you dread into a routine you barely notice.
Worked example
A Nelson café files GST two-monthly. In a typical period it takes $115,000 including GST and spends $57,500 including GST on claimable costs. Last year's RIT was $24,000.
| Item | Calculation | Amount |
|---|---|---|
| GST on sales | $115,000 × 3/23 | $15,000 |
| GST on expenses | $57,500 × 3/23 | $7,500 |
| GST to pay for the period | $7,500 | |
| Provisional tax (standard) | $24,000 + 5% | $25,200 |
| Each of three instalments | $25,200 ÷ 3 | $8,400 |
| Weekly set-aside | $7,500 ÷ 8.7 + $25,200 ÷ 52 | about $1,350 |
What the planner doesn't cover
- PAYE and employer deductions — these are usually paid twice a month or monthly and are best handled through payroll software.
- Terminal tax — if this year's profit is higher than last year's, extra tax may be due after year-end (usually 7 February, or 7 April with a tax agent's extension).
- Other provisional tax options — estimation, ratio and AIM work differently. Our provisional tax guide compares them.
- Payments vs invoice basis — the timing of GST depends on your accounting basis. See GST filing periods and cash planning.
If you're already behind
If an instalment or GST return has already been missed, penalties and interest start building. You can ask Inland Revenue for an instalment arrangement, or clear the balance with a business loan — with a property-secured loan, IRD debt can be refinanced or paid out. Read dealing with IRD debt or see IRD tax debt funding. The planner runs in your browser; nothing is stored or sent.