The self-lodgement tax deadline falls on 31 October every year, closing the four-month window that opened on 1 July. 17 October 2030 falls inside October, the final month of that window, in the fourth calendar quarter of 2030, with the deadline drawing closer as the month progresses.
A public holiday landing on a Thursday sits one day short of the weekend, and workers commonly take the Friday after it as annual leave to turn a single day off into a four-day break. Thursday 17 October 2030 falls on this day of the week, one working day ahead of Friday and two ahead of the weekend that follows it.
2030 has 365 days on the calendar. Leap years add a single extra day to February, giving those years 366 days instead of 365 and shifting the day-of-year number for every date from March onward by one compared with an ordinary year. This is the only irregularity in the length of the Australian calendar year.