Western Australia marks King's Birthday on the last Monday of September, months after every other state observes the same public holiday name. 20 September 2028 carries this public holiday only in Western Australia, with the rest of the country working through an ordinary day under a completely different holiday calendar for the same occasion.
The Ekka public holiday in greater Brisbane is held on a Wednesday during the Royal Queensland Show each August, one of the few recurring public holidays fixed to this day of the week. Wednesday 20 September 2028 falls on the same weekday as this regional observance, which applies only within greater Brisbane and not to the rest of Queensland.
2028 has 366 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.