Open a wall calendar in New York and the first column is Sunday. Open one in London, Berlin or Sydney and it is usually Monday. Neither is wrong — they come from different traditions — but picking the right one makes a calendar much easier to use.
Sunday-first calendars
In the Jewish and Christian traditions Sunday is the first day of the week, and that convention survives in calendars in the United States, Canada, Japan and several other countries. Most US printed calendars, school planners and many phone apps set to US English start on Sunday.
Monday-first calendars
The international standard ISO 8601 defines Monday as the first day of the week, and it is the norm in the UK, Ireland, most of Europe, Australia and New Zealand. If you think of the week as “work days, then the weekend”, a Monday start keeps Saturday and Sunday together at the end of each row. It is also required if you use ISO week numbers.
How to choose
- Match what people around you use. A family or office calendar should follow the local convention, so nobody misreads a date.
- Planning work weeks? Monday first keeps each work week on one row.
- Planning around the weekend? Sunday first splits the weekend across both ends of each row, so every week is “bookended” by days off — some people find that easier to read.
- Using week numbers? Choose Monday.
Switching on this site
Every calendar has a “Week starts” option. The US calendars default to Sunday and the UK calendars to Monday, and your choice is remembered on your device. Try it on the 2026 calendar or the 2026 UK calendar.