CALENDAR GUIDE
It depends on where you are. The international ISO 8601 standard defines Monday as the first day of the week. But the United States, Canada, much of Latin America, and Japan traditionally start their week on Sunday.
| First day of week | Countries / Regions |
|---|---|
| Monday | Most of Europe, UK, Australia, China, Russia, most of Africa, ISO 8601 standard |
| Sunday | United States, Canada, Mexico, Brazil, Japan, South Korea, most of Latin America |
| Saturday | Some Islamic countries (Maldives, Afghanistan) |
The difference traces back to two traditions:
This difference affects how calendars display weeks:
=WEEKDAY(A1, 2) uses Monday=1 (ISO mode)ISO 8601 defines Monday as day 1 and Sunday as day 7. This is the international standard used in business, logistics, and most of Europe.
The US convention traces back to the Judeo-Christian tradition where Sunday is the first day of the new week, following the Sabbath (Saturday).
Google Calendar defaults to Sunday in the US locale. You can change it in Settings → View options → Start week on → Monday.
In the Bible, Sunday is the first day of the week. Genesis describes God resting on the seventh day (Sabbath = Saturday), making Sunday the start of the new week.