The self-lodgement tax deadline falls on 31 October every year, closing the four-month window that opened on 1 July. 11 October 2027 falls inside October, the final month of that window, in the fourth calendar quarter of 2027, with the deadline drawing closer as the month progresses.
Monday 11 October 2027 is the first working day of its week. Any bill, deadline or rostered task set for the preceding Saturday or Sunday moves to this date under standard business-day rules, and the working-day count above treats it as day one of a fresh five-day working stretch that runs through to Friday, before the weekend resets the cycle again.
The quarter containing 11 October 2027 is based on the calendar year running January to December, a separate system from the Australian financial year, which runs from 1 July to 30 June and splits into its own four quarters. Businesses often track both systems side by side, one for tax filings and one for calendar-year planning.