Is the week’s first day Monday or Sunday? The answer depends on where you live, your faith tradition, and even the software you use. Understanding how countries define the start of the week helps you plan meetings, run payroll correctly, and align school calendars across regions without surprises.

This guide compares global conventions, explains their roots, and shows the practical impact on scheduling, payroll, and education—plus what to do when your team spans different week-start cultures.

What does “start of the week” actually mean?

People use “start of the week” in a few ways, often mixing them up. It helps to separate three related concepts:

  • First day of the week (calendar): The day calendars display in the leftmost column or at the top of a week. This is a cultural or standards-based convention (e.g., Monday under ISO-8601).
  • Start of the workweek: The first working day in a typical business week (e.g., Monday in most of Europe, Sunday in parts of the Middle East).
  • Weekend composition: The days considered “off.” Many countries use Saturday–Sunday; others use Friday–Saturday or Friday half-day plus Saturday–Sunday.

ISO-8601, the international date standard, defines Monday as the first day of the week. That standard is widely used in Europe and by many global businesses, but local laws and traditions can still define the week differently.

Who starts on Monday, who on Sunday (and who on Saturday)?

There isn’t a single global rule. Instead, conventions cluster by region, tradition, and market alignment.

Common Monday-start regions

  • Europe: Most European countries follow ISO-8601 (Monday start). Week numbers are often used in business and schools.
  • Latin America: Many Spanish- and Portuguese-speaking countries show Monday as the first day in calendars and business settings.
  • Africa and Asia (broadly): A majority of locales adopt Monday starts in modern software and government calendars, especially where ISO conventions are preferred.
  • International organizations: Standards bodies, airlines, logistics, and global project teams frequently default to Monday for clarity across borders.

Common Sunday-start regions

  • United States and Canada: Many printed calendars and default device settings show Sunday first. Some businesses still schedule around a Sunday-start week.
  • Parts of the Caribbean and Pacific: Sunday-first layouts are common in consumer calendars, though enterprise systems may vary.
  • Faith-driven communities worldwide: In traditions where Sunday is a distinct sacred day, calendars historically begin with Sunday.

Saturday-start locales

  • Some Middle Eastern settings: In regions where the core workweek is Sunday–Thursday or where Friday–Saturday constitute the weekend, local calendars or software configurations may use Saturday as the first day to align the view with the business week.

Note: The Unicode CLDR (Common Locale Data Repository), used by major operating systems and apps, encodes “first day of week” by locale. It shows a majority of locales use Monday, Sunday starts are concentrated in North America and a handful of others, and Saturday starts appear in parts of the Middle East. Your phone or laptop likely follows this data based on your region settings.

Why countries disagree: roots of the convention

Religious tradition

  • Judeo-Christian heritage: Sunday has long been considered the “first day” theologically, with Saturday (Sabbath) as the seventh. Many Christian-influenced calendars therefore put Sunday first.
  • Islamic practice: Friday is central for congregational prayer, so many countries historically structured weekends around Friday–Saturday, influencing whether calendars start on Saturday or Sunday to frame the workweek.

Standardization and global trade

  • ISO-8601: Monday-start weeks and week-numbering harmonize cross-border coordination, especially in manufacturing, logistics, and software.
  • Market alignment: As economies integrate, some countries adjust workweeks or calendar conventions to sync with financial markets and global partners.

Colonial and administrative legacy

  • Former colonies often inherited calendar norms from administrators or missionaries, later reshaped by local policy or international standards.

Software defaults

  • CLDR-driven systems: iOS, Android, Windows, macOS, and major web frameworks use locale data to pick the first day of week automatically.
  • Product-specific settings: Tools like Google Calendar, Microsoft Outlook, Slack, Jira, and Trello let users override the week start, but company-wide defaults still guide behavior.
  • File formats and rules: iCalendar (RFC 5545) recurrence rules include WKST=MO or WKST=SU to pin the week boundary for repeating events.

Scheduling: how the week’s first day changes the plan

Small differences at the calendar boundary can derail coordination. Watch for:

  • Meeting planning: Weekly standups may fall on different “week” labels. A Monday-start calendar groups Sat–Sun together at the end; a Sunday-start pushes Saturday to the tail of the prior week.
  • Recurring events: “Every other week” sequences depend on which week you consider the first. Always specify the anchor date and week start (e.g., WKST=MO).
  • Travel and rosters: Airline rotations, hotel stays, and shift rosters can cross midnight/week boundaries; ensure shared calendars use a common standard.
  • Analytics and reporting: Weekly dashboards, sales reports, and marketing cohorts shift if the week boundary moves. A Sunday-start and Monday-start can produce different totals for the “same” week.
  • Software behavior: Functions like Excel’s WEEKNUM or SQL date routines have parameters for the week start. Mismatches lead to silent inconsistencies.

Payroll: the legal and financial stakes

Week definition isn’t just cosmetic—it can be a compliance issue.

  • United States (FLSA): The Fair Labor Standards Act defines a workweek as any fixed, recurring 168-hour period. Employers may choose any start day and time (e.g., Sunday 12:00 a.m. to Saturday 11:59 p.m.), but must apply it consistently for overtime calculations.
  • State and provincial rules: Some jurisdictions have additional weekly overtime thresholds or industry-specific rules. Changing the defined workweek start can affect eligibility and premiums.
  • European Union: The Working Time Directive refers to a seven-day reference period but does not universally impose a specific start day. National law and collective agreements fill in details.
  • Middle East and North Africa: Where the working week differs (e.g., Sunday–Thursday or Monday–Friday hybrids), payroll systems often align the pay week with the local workweek to ensure clean overtime and allowance calculations.
  • Public holidays and weekends: Whether a holiday lands within a pay week or bridges weekends can affect holiday pay, time-in-lieu, or shift differentials—especially for retail and hospitality.

Best practice for payroll:

  • Define the official workweek boundary in policy and your HRIS/payroll system.
  • Document how weekly overtime is computed and which timezone applies for cross-border teams.
  • Lock the workweek start during pay periods; if changes are needed, implement them prospectively with clear employee notice.

School calendars: timetables and week numbers

Education systems rely on a predictable week structure for instruction, exams, and attendance. Two details matter most:

  • First day of the school week: In many countries, classes start Monday; in others, Sunday is a normal school day. Calendars, bus schedules, and campus facilities must reflect the local pattern.
  • Week numbering: ISO week numbers (Week 1 to Week 52/53) start on Monday, and Week 1 is the week with the year’s first Thursday. This system is common in European planning documents and can reduce ambiguity in syllabi and exam timetables.

For international programs and exchange students, publishing both the local day names and the ISO week numbers helps prevent miscommunication.

How week starts affect everyday operations

  • Retail promotions: “This week’s deals” can begin Sunday in North America but Monday in Europe; reconcile promotion calendars for global e-commerce.
  • Customer support SLAs: If you promise resolution within “one business week,” define what that means by region and clarify whether the week includes Friday in places with Friday–Saturday weekends.
  • Project management: Sprint boards and burndown charts look different when the iteration boundary shifts. Agree on a common week anchor to stabilize metrics.
  • Data warehousing: Store timestamps in UTC and maintain a dedicated “week key” for reports (e.g., ISO week-year and week number) rather than computing on the fly per user locale.

Designing policies and systems that won’t bite later

  • Be explicit: In docs and UIs, say “Monday–Sunday” or “Sunday–Saturday” instead of “weekly.” Add tooltips for week numbering rules.
  • Allow configuration: Let users or admins pick the first day of the week. Respect locale defaults but support overrides for payroll and operations.
  • Pin recurrence rules: When creating repeating events, set the week start (e.g., WKST=MO) and include the timezone. Avoid ambiguity in “every 2 weeks” patterns.
  • Train and communicate: For cross-border teams, publish a short guide explaining your organization’s week definition, payroll cutoff, and holiday treatment.
  • Test analytics: Validate weekly reports under multiple week-start settings to ensure figures remain consistent with policy.

Mini-scenarios: how it plays out

Global product launch

A marketing team schedules “Week 1” deliverables. The U.S. team works Sunday–Saturday; the German team works Monday–Friday and uses ISO week numbers. Without alignment, the U.S. counts Sunday as part of Week 1 while Germany begins Monday—one day out of sync. Solution: adopt ISO week numbers and a Monday-start for internal planning, while local retail campaigns can still start Sunday in North America.

Payroll cutoff and overtime

A retailer in Canada pays weekly and defines the workweek as Sunday–Saturday. If an employee works a late Saturday shift that runs past midnight, hours after midnight belong to the next week. Payroll must apply the defined boundary consistently; otherwise, overtime could be miscalculated.

University term planning

An international university publishes a timetable using ISO Week 36–Week 50, Monday-start. Exchange students from the U.S. initially expect Sunday-first weeks. The university’s calendar app clarifies the Monday start and highlights local public holidays that fall on Fridays, ensuring labs and exams aren’t accidentally scheduled on off days.

Key takeaways

  • The “start of the week” varies by culture, law, and software defaults.
  • ISO-8601 sets Monday as the first day, and many countries follow it; Sunday-start remains common in North America.
  • Week boundaries affect scheduling, payroll compliance, retail promotions, analytics, and education.
  • Define your organization’s week explicitly, configure systems accordingly, and communicate clearly across teams.

FAQ

Which countries start the week on Sunday?

Sunday-first calendars are common in the United States and Canada and appear in some Caribbean and Pacific locales. Many faith communities worldwide also prefer Sunday-first layouts. However, enterprise systems in these regions may still support Monday-first for consistency with international partners.

Which countries start the week on Monday?

Most European countries, many in Latin America, and a broad set across Africa and Asia use Monday as the first day. ISO-8601 reinforces this pattern, and it’s the default in many global organizations and software tools.

Why does ISO-8601 choose Monday?

ISO-8601 aims to standardize dates and times across borders. A Monday-start aligns with widespread European practice, simplifies week numbering, and reduces ambiguity in international business, logistics, and data analysis.

Does the start of the week affect payroll?

Yes. In places like the U.S., the defined workweek (a fixed 168-hour window) determines overtime. Employers can choose the start day but must apply it consistently. Elsewhere, national law or collective agreements shape the pay week. Always document your official workweek and align your payroll system to it.

Can we pick a different week start for our company?

Often yes, especially for internal planning. For payroll and compliance, you must follow local laws and your published policy. For calendars and project tools, choose a standard (many pick Monday) and allow teams to view local layouts if needed.

What about countries with Friday–Saturday weekends?

In regions where Friday is a main day of worship and rest, weekends commonly include Friday–Saturday, and the business week may run Sunday–Thursday. Calendar apps in these locales may use Saturday or Sunday as the displayed week start so workdays appear together.

How do week numbers work?

ISO week numbers start on Monday. Week 1 is the week containing the first Thursday of the year (or, equivalently, January 4). Week numbers are widely used in Europe for manufacturing schedules, education, and project plans.