⚖️ Comparison · Updated for 2026
UK Week Start (Monday) vs US Week Start (Sunday)
Side-by-side comparison, when-to-use-each guide, and instant conversion. Reviewed for 2026.
Quick answer: UK and most of Europe: the calendar week starts Monday (ISO 8601 standard). US, Canada, Japan: the week starts Sunday. This affects calendars, payroll, school timetables and any software calculating 'this week' or 'last week'.
Decision guide — when to use which
Use UK Week Start (Monday) when…
UK, Europe, Australia, ISO 8601, business calendars worldwide.
Use US Week Start (Sunday) when…
US, Canada, Japan, Mexico, Brazil. Most US-built software defaults to Sunday-first.
📊 Side-by-side comparison
| 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
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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.
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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.
Reviewed for 2026. All conversion factors and historical references verified against official sources (ISO standards, government weights & measures legislation, IEC technical specifications). Built by a UK-based qualified primary teacher and FA Level 2 coach as part of 247QuickTools' free utility-tools project. We don't sell SEO links or accept paid placements in this content.