UK Week Start (Monday) vs US Week Start (Sunday)
Side-by-side comparison, when-to-use-each guide, and instant conversion. Reviewed for 2026.
UK, Europe, Australia, ISO 8601, business calendars worldwide.
US, Canada, Japan, Mexico, Brazil. Most US-built software defaults to Sunday-first.
| Aspect | UK Week Start (Monday) | US Week Start (Sunday) |
|---|---|---|
| Standard | ISO 8601 | Various religious and historical |
| Calendar apps | Apple/Google use locale default | Apple/Google use locale default |
| Day 1 | Monday | Sunday |
| Day 7 | Sunday | Saturday |
| Used by | UK, EU, Australia, NZ | US, Canada, Japan, Mexico, Brazil |
Frequently asked
What does ISO 8601 say?
ISO 8601 mandates Monday as day 1, Sunday as day 7. This is the standard for international business and most calendar software's 'professional' settings.
Why does the US start week on Sunday?
Inherited from Christian tradition (Sunday was the Sabbath, day of rest, first day of week in the Roman calendar). The UK adopted the Monday-first convention in the 20th century for industrial workweek alignment.
Frequently asked questions
What does ISO 8601 say?
ISO 8601 mandates Monday as day 1, Sunday as day 7. This is the standard for international business and most calendar software's 'professional' settings.
Why does the US start week on Sunday?
Inherited from Christian tradition (Sunday was the Sabbath, day of rest, first day of week in the Roman calendar). The UK adopted the Monday-first convention in the 20th century for industrial workweek alignment.