What's the First Day of the Week? Country-by-Country Conventions

Last reviewed on 2026-05-09

Open a wall calendar in London and the week starts on Monday. Open the calendar app on a phone bought in Dallas and the same week starts on Sunday. Walk into a printing shop in Cairo and you may find calendars that begin on Saturday. None of these is wrong — they reflect a long-standing disagreement about which day deserves to be called first. This page lays out the three main conventions, the standards that govern them, and the countries that follow each.

The three conventions in use today

There are essentially three answers in active use:

Monday-first. The international standard ISO 8601 defines Monday as the first day of the week. This is the convention used in most of Europe, the United Kingdom, China, and a long list of countries that have adopted ISO time-and-date norms for business and software.
Sunday-first. A tradition rooted in Jewish, Christian, and broader Abrahamic religious calendars, where the day of rest (Sabbath/Saturday or Sunday) closes the week and the day after begins a new one. This is the day-one convention in the United States, Canada, Brazil, Japan, Israel, and many Latin American and East Asian countries.
Saturday-first. Used primarily in countries where Friday is the holy day and the working week begins on Saturday — for example Egypt, Saudi Arabia, the United Arab Emirates (with recent shifts), and several other Arab states.

What ISO 8601 actually says

ISO 8601 is the standard most software and international business uses to talk about dates and times. Section 4.3.2.2 defines the calendar week as starting on Monday, and numbers weeks accordingly: the first week of the year is the one that contains the first Thursday of January. That is why a "week 1" in an international project plan can begin in late December or early January — and why the same date can fall in different ISO weeks depending on where January's Thursdays land.

ISO 8601 doesn't override anyone's calendar tradition. It is a coordination tool. National calendars, religious calendars, school calendars, and personal preferences continue to use whatever convention they always have.

Where each convention is used

First day	Examples of countries / contexts	Typical reason
Monday	Most of Europe (UK, Ireland, France, Germany, Italy, Spain, the Nordic countries, Poland, Russia), China, India (in many calendars), Australia and New Zealand (mixed), most international software defaults.	ISO 8601 alignment; a working-week orientation in which the weekend ends the week.
Sunday	United States, Canada, Brazil, Mexico (mixed), Japan, the Philippines, much of Latin America, Israel, many Christian and Jewish liturgical contexts.	Religious calendars in which Saturday or Sunday is the day of rest and the following day begins the cycle anew.
Saturday	Egypt, Saudi Arabia, several other Arab states (the UAE shifted to a Monday–Friday working week in 2022 but Saturday-first calendar entries persist).	Friday is the day of congregational prayer (jumu'ah) and the holy day; the working week begins the day after.

Note the difference between calendar convention (what your printed calendar shows) and working week (the days an office is open). They line up in many countries but not all. Several Gulf states use Sunday–Thursday or Monday–Friday as the working week while keeping a Saturday-first calendar.

How language reflects the convention

Some languages encode the convention into the day names themselves:

Portuguese numbers the days from segunda-feira (second day, Monday) through sexta-feira (sixth day, Friday). Sunday (domingo) is the first, Saturday (sábado) the seventh — a Sunday-first system baked into the vocabulary.
Hebrew uses yom rishon (first day) for Sunday and yom shabbat for Saturday — clearly Sunday-first.
Arabic day names like al-ahad (the first/one) for Sunday and al-sabt (the seventh) for Saturday again encode a Sunday-first numbering, even in countries that operate a Saturday-start working week.
See our guide to numbered vs. named day systems, the Hebrew page, and the Arabic page for the full sets.

By contrast, Romance languages other than Portuguese, plus the Germanic and Slavic languages, derive their day names from gods or planets and don't encode a numbered position at all. The convention then comes from civil and religious calendars rather than from the words.

Why this matters in practice

Software and spreadsheets

If you've ever wondered why Excel sometimes treats Sunday as day 1 and sometimes Monday, the answer is the WEEKDAY function's optional argument. The default in many regional builds returns Sunday=1; ISO mode returns Monday=1. The same applies to strftime in many programming languages: %w typically counts Sunday as 0, while %u counts Monday as 1 (ISO).

Calendar apps and digital products

Most modern apps let you choose which day starts your week — Apple Calendar, Google Calendar, Outlook, and Linux desktops all expose this setting. The default is normally inherited from the device's regional setting, which is why an iPhone bought in the US shows Sunday-first and one bought in the UK shows Monday-first.

Travel and bookings

Hotel calendar widgets, flight schedules, and rental booking tools may display weeks differently depending on where the property or company is based. If a "weekly rate" is described, it is worth confirming whether the week is being counted Monday–Sunday or Sunday–Saturday, especially when transitioning between weekend and midweek bookings.

Project planning across borders

Multinational teams almost always default to ISO weeks for project planning to avoid ambiguity. "Week 27" means the same thing in Frankfurt, São Paulo, and Tokyo when ISO 8601 is in force.

A short history of the disagreement

Both Sunday-first and Monday-first conventions are old. The Jewish calendar, the Christian liturgical calendar, and the Roman planetary system all begin counting from the day of the Sun (Sunday) — making Sunday the natural day one in long stretches of Western history. Monday-first is the newer convention in popular use; it gained traction in the twentieth century because the workplace pattern of Monday-to-Friday with a two-day weekend made Monday feel like the start of the week. ISO 8601, first published in 1988, formalised that intuition for international standardisation.

The Saturday-first convention reflects the Islamic week, in which Friday's congregational prayer marks the day's importance and the working week resumes the day after. As Muslim-majority countries have integrated more deeply into international business, several have shifted their working week to Monday–Friday or Sunday–Thursday while preserving Saturday-first calendars and Friday holy days.

Common-confusion checklist

Before you assume which convention applies, check the following:

Where is the calendar published? A US-published calendar is almost certainly Sunday-first; a European one Monday-first.
Whose week is being numbered? ISO week numbers and locale-default week numbers can differ by one.
Is the device's regional setting up to date? Travelling with a phone whose region doesn't match where you are can produce surprising calendar layouts.
Are working week and calendar week aligned? Especially in the Gulf, the two can diverge.