The provisional tax due dates are established in the Income Tax Act 2007, specifically in: Section RC 9(2) and (3).
These sections reference Schedule 3, Part A, Columns B, D, and F, which for the month of March as the month of balance date, correspond to the following calendar dates: 28 August, 15 January, 7 May.
It’s not uncommon for a tax agent to finalize a client’s tax return as late as 31 March of the following year, especially under extension of time (EOT) arrangements. This means that by the time the taxpayer's final tax position is determined, the first or even second provisional tax payment may be past. If the latest available assessment is not from the immediate preceding year, IRD allows tax to be calculated based on the tax year before the preceding year, uplifted by 10%.