Turnover is calculated from GST returns as the sum of gross sales in the year ended 31 March. For a 2-monthly filer, this would mean the sum of gross sales on 6 successive GST returns, with the last return being for the period ending 31 March.
The GST data only include GST collected or refunded by Inland Revenue. GST collected on imports by the New Zealand Customs Service is not included.
The data for these statistics is available for download from the link at the bottom of the page.
Graph of the number of GST filers by turnover band

The graph has 5 lines showing the number of GST filers by turnover band from March 2007 to March 2021.
In the latest year, 2021, the number of customers filing Inland Revenue GST grew significantly by 4.2%. The previous 4 years averaged 1% growth per year.