⚖️ 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 Judeo-Christian tradition, where Sunday is counted as the first day of the week. UK diaries and calendars commonly start on Monday, in line with ISO 8601 and the working week.

Reviewed for 2026. This comparison is general guidance based on publicly available information. Prices, rates, rules and specifications change, so check current details with the provider or an official source before making a decision. 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.

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 Judeo-Christian tradition, where Sunday is counted as the first day of the week. UK diaries and calendars commonly start on Monday, in line with ISO 8601 and the working week.