GST Instalment Payer Calculator

GST Instalment Payments in New Zealand

Some GST-registered businesses, particularly smaller ones on six-monthly filing, can opt to pay GST in instalments rather than filing a full return each period. This simplifies compliance because you don't need to calculate your actual GST position for each period. Instead, you pay an estimated amount based on prior year figures, and do a wash-up in your final return for the year.

The Ratio Method

The ratio method calculates your instalment as a percentage of your current period's sales, using the ratio of GST paid to sales from the prior year. If you paid $12,000 GST on $200,000 in sales last year, your ratio is 6%. If your sales this period are $35,000, your instalment is $35,000 x 6% = $2,100. This method adjusts naturally for seasonal variations in turnover.

The Estimation Method

The estimation method simply divides your prior year's total GST by the number of instalment periods. If you paid $12,000 last year and file six-monthly, each instalment is $6,000. This is simpler but doesn't account for growth or seasonal patterns. If your business is growing, you may underpay and face a wash-up bill (plus use-of-money interest) at year end.

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Last updated: April 2026 | Rates current for the 2026/27 tax year