Reference
Three week-numbering systems cover most calendars in use today. Pick the one your business or software follows.
ISO 8601
The international standard for week numbering used in software, finance, and European business.
AU Financial Year
Week numbering aligned to the Australian financial year (1 July – 30 June), used by the ATO and Australian businesses.
US Standard
Sunday-start week numbering used by US payroll, retail, and Microsoft Excel's default WEEKNUM function.