How GST taxable periods are decided

MIRA's three-monthly taxable periods are the calendar quarters: January to March, April to June, July to September, and October to December. There is nothing to configure and nothing to choose — a purchase belongs to the period its invoice date falls in.

The complication is not the rule but the paperwork. Invoices arrive late, get photographed in batches, and are entered in the order they turned up rather than the order they were issued. An invoice dated 29 June that reaches your desk in July belongs to the second quarter, and filing it in the third is a misstatement in both returns.

Why the date is read, not chosen

In this product the period is derived from the invoice date inside the database rather than stored as a separate field that someone sets. A stored quarter can be edited, imported wrongly, or left behind when a date is corrected. A derived one cannot drift from the document it describes.

Dates are also handled as plain YYYY-MM-DD text throughout, never as timestamps. A timestamp carries a timezone, and a timezone is how an invoice dated 1 July quietly becomes a 30 June invoice on a server in a different part of the world.

When the return is due

The statement is due on the 28th of the month following the end of the period. So the fourth quarter of 2025, October to December, is due on 28 January 2026. Where that date lands on a public holiday MIRA extends it to the next working day, so treat the 28th as the earliest deadline rather than the only one.