First Day of the Week by Country: Why Calendars Start on Different Days

Open a wall calendar in Chicago and the grid begins with Sunday. Open one in Berlin and the same seven days begin with Monday. Fly to Cairo and printed calendars may start the row on Saturday. Nobody is making a mistake. The world has never agreed on which day deserves to be called first, and the disagreement is old enough that it now sits baked into software, payroll systems, and international standards.

This guide covers what the first day of the week is by country, where each convention came from, and why the split still causes real problems for anyone scheduling work across borders.

Four different answers are in use right now

There is no single global rule, but there are only four answers in active use.

Monday. The international standard ISO 8601 makes Monday day one and Sunday day seven. This is the most widely used convention in the world.

Sunday. Standard across almost all of North and South America, and used in Japan, Israel, India, and much of Southeast Asia and southern Africa. Europe and Oceania treat Sunday as the last day instead.

Saturday. Used across much of the Middle East and North Africa, where the working week historically ran Sunday to Thursday.

Friday. Used in exactly one country: the Maldives.

The most reliable public dataset on this is the Unicode Common Locale Data Repository (CLDR), which maintains a firstDay value for every territory. That file is what most operating systems, phones, and programming languages read when they decide how to draw a calendar grid for your region. The current release (CLDR 48) lists explicit entries for roughly 149 territories, and any territory not listed falls back to the world default, which is Monday.

First day of the week by country

The table below is drawn directly from the CLDR weekData file rather than from secondary sources, so it reflects the values software actually uses.

| Start day | Countries and territories | Count | |---|---|---| | Monday | United Kingdom, Ireland, France, Germany, Spain, Italy, Netherlands, Belgium, Switzerland, Austria, Sweden, Norway, Denmark, Finland, Poland, Czechia, Slovakia, Hungary, Romania, Bulgaria, Greece, Serbia, Croatia, Ukraine, Russia, Belarus, Turkey, Cyprus, China, Vietnam, Malaysia, Australia, New Zealand, Argentina, Chile, Uruguay, Ecuador, Costa Rica, United Arab Emirates, Lebanon, Sri Lanka, Kazakhstan, Uzbekistan, Georgia, Armenia, Azerbaijan, and others | 78 listed, plus every unlisted territory | | Sunday | United States, Canada, Mexico, Brazil, Colombia, Peru, Venezuela, Panama, Paraguay, Guatemala, Honduras, Nicaragua, El Salvador, Dominican Republic, Jamaica, Bahamas, Belize, Trinidad and Tobago, Puerto Rico, Japan, South Korea, Taiwan, Hong Kong, Macau, Singapore, Thailand, Indonesia, Philippines, India, Pakistan, Bangladesh, Nepal, Bhutan, Cambodia, Laos, Myanmar, Israel, Saudi Arabia, Yemen, Portugal, Malta, Iceland, South Africa, Kenya, Ethiopia, Zimbabwe, Mozambique, Botswana, Samoa, Guam, American Samoa, US Virgin Islands | 56 | | Saturday | Afghanistan, Algeria, Bahrain, Djibouti, Egypt, Iran, Iraq, Jordan, Kuwait, Libya, Oman, Qatar, Sudan, Syria | 14 | | Friday | Maldives | 1 |

Two entries in that data are worth flagging because they surprise people. Portugal starts the week on Sunday despite sitting in Western Europe. And the United Kingdom carries a formal alternate value of Sunday alongside its Monday default, which is CLDR's way of recording that both conventions genuinely circulate there.

Why the disagreement exists at all

The week is the one calendar unit with no natural anchor

A day is one rotation of the Earth. A month roughly tracks the moon. A year tracks the sun. Seven days tracks nothing. Because the week is a human invention rather than an astronomical fact, there was never a physical event to point at and say "the week starts here." Every answer is a cultural decision.

The cycle itself traces back to Mesopotamia, where astronomers tracked seven moving objects in the sky: the Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn. Babylonians marked the 7th, 14th, 21st, and 28th days of the lunar month as special, with activity restrictions for officials, while Judaism developed the continuous seven-day cycle that ran independently of lunar phases, a practice dating to the 6th century BC at the latest.

Sabbath arithmetic put Sunday first

If the day of rest is the seventh day, then the day after it is the first. That single piece of logic is the origin of the Sunday-first convention, and it survives in the United States today.

Rome initially used a different system. Seven-day and eight-day weeks coexisted until Emperor Constantine made the seven-day week official in AD 321, after which it spread throughout the Roman Empire and eventually through Christian cultures worldwide. Sunday remained the first day, treated as the day of the sun god Sol Invictus and the Lord's Day, while the Jewish Sabbath remained the seventh, and Constantine's 321 CE decree made dies Solis a legal holiday.

American calendars inherited that arrangement and never changed it.

Friday prayer moved the start to Saturday

In much of the Middle East and North Africa, the pivot day is Friday rather than Saturday or Sunday. Where Friday functions as the communal day, the working week naturally ran Sunday through Thursday, and Saturday sat at the head of the cycle. That is why Egypt, Iraq, Jordan, Kuwait, Qatar, and their neighbors carry a Saturday firstDay value.

Notice that these countries are not following religious doctrine about day numbering so much as following the shape of the working week. That distinction matters for the next section.

Monday-first is an industrial-era idea

The Monday convention is far newer than the other two. It comes from the five-day working week and the invention of the weekend, not from antiquity. Once Saturday and Sunday were grouped together at the end as leisure time, putting Monday at the head of the grid became the arrangement that matched how people actually lived. ISO 8601 later encoded that arrangement as the international default.

This is why the Sunday-first convention feels internally inconsistent to a lot of people. If Saturday and Sunday together form the "weekend," it is odd for Sunday to also be the beginning. The US convention makes sense historically and stops making sense the moment you apply weekend logic to it.

What ISO 8601 actually says

ISO 8601 is the international standard for writing dates and times. It is maintained by the International Organization for Standardization, was first published in 1988, and has been updated in 1991, 2000, 2004, and 2019, with an amendment in 2022. It exists because dates are written differently around the world: in Europe the day comes before the month, so April 15 is 15/4, while in North America the month comes first, giving 4/15.

Two rules matter here.

Monday is day 1. Sunday is day 7. This is fixed and does not vary by locale.

Week 1 is defined by Thursday, not by January 1. ISO 8601 defines the calendar week as seven days beginning on a Monday, and the first calendar week of a year as the one that includes the first Thursday of that year. That is the same as saying week 1 always contains January 4.

The consequence catches people out every January. Week 1 sometimes begins on a Monday in the last few days of December, and week 52 sometimes ends on a Sunday in the first few days of January.

The US does it differently. In the American system, week 1 is simply the week containing January 1. CLDR records this as a minDays value: the United States uses 1, meaning a single day in the new year is enough to make a week count, while Germany, France, the UK, Spain, Italy, and most of Europe use 4, matching the ISO rule.

Day names still carry the old counting

Language preserves the argument even where calendars have moved on. Several major languages number their weekdays, and the numbering starts from Sunday.

A tradition of numbering the days rather than using planetary names produced "second day" for Monday across several languages: Hebrew yom sheni, Greek Deutera, Latin feria secunda, and Arabic al-ithnayn.

Portuguese follows the same pattern, with weekday names built from ordinals: segunda-feira for Monday (second day), then terça, quarta, quinta, and sexta-feira. Arabic weekdays are similarly numeric, with al-ahad as day one for Sunday and al-ithnayn as day two for Monday.

Hebrew has no special names for the days of the week at all except Saturday (Shabbat), with Sunday simply called "the first day."

So Portuguese literally calls Monday "the second day" while Portugal's calendar software starts the week on Sunday. The language and the data agree in that case. But Arabic-speaking Egypt calls Sunday "day one" while its calendar convention starts on Saturday, because the working week overrode the naming. The two systems drifted apart.

These conventions change more often than you think

Week-start conventions are not fossilized. They move when working weeks move.

CLDR itself has revised entries. In CLDR release 34, the maintainers changed the firstDay value for Portugal from Monday to Sunday.

The clearest recent example is the United Arab Emirates. In December 2021, the UAE announced that all government entities would adopt a four-and-a-half-day working week, with Friday afternoon, Saturday, and Sunday forming the new weekend, effective January 1, 2022, moving the country in line with Western schedules. The UAE had previously run a Friday to Saturday weekend, matching other countries in the region. Schools and universities also moved to a Monday to Friday schedule on the same basis.

Today the UAE carries a Monday firstDay value in CLDR, sitting alongside European countries rather than its regional neighbors. Saudi Arabia, meanwhile, is recorded as Sunday-first with a Friday to Saturday weekend, a combination that fits neither the American nor the ISO pattern cleanly.

If you maintain software with hardcoded regional assumptions, this is the practical takeaway: the data changes, so read it rather than hardcoding it.

Where the split actually causes problems

For most people this is trivia. For anyone running reports, payroll, or scheduling across countries, it produces genuine errors.

The most common failure is in spreadsheets. Excel ships two different week-numbering functions and they do not agree.

| Function | Week starts on | How week 1 is defined | |---|---|---| | WEEKNUM (default) | Sunday | The week containing January 1 | | WEEKNUM with return type 21 | Monday | ISO 8601 rule | | ISOWEEKNUM | Monday | The week containing the first Thursday |

Microsoft documents the difference plainly. There are two systems: System 1 treats the week containing January 1 as week 1, while System 2 uses the week containing the first Thursday of the year, which is the methodology specified in ISO 8601. The default return type is 1, meaning the week begins on Sunday.

Microsoft also warns that for years where three days or less fall in the first week of January, WEEKNUM returns week numbers that are incorrect according to the European standard.

The result is a spreadsheet that quietly reports different week numbers to a US office and a German office for the same date range. Nobody sees an error message.

The same class of problem shows up elsewhere:

• Weekly dashboards where a US-built report and an EU-built report disagree on which sales landed in which week
• Recurring meeting invites that shift when a calendar's week-start setting differs between attendees
• Payroll periods that appear to gain or lose a day at year boundaries
• Shift rotas built on "week starts Monday" logic and then rendered on a Sunday-first grid

If you just want your own calendar to show the number instead of calculating it by hand, see how to show week numbers in Google, Outlook, and Apple Calendar.

How to pick a convention and stay consistent

A few practical rules cover almost every case.

1. For anything technical, machine-readable, or cross-border, use ISO 8601. Monday first, week 1 contains the first Thursday. It is unambiguous and it sorts correctly.
2. For anything user-facing, follow the reader's locale. Show a Sunday-first grid to a US audience and a Monday-first grid to a European one. Do not force a standard on people reading a wall calendar.
3. Never hardcode a week-start day. Read it from CLDR or from your platform's locale API, because the underlying data changes.
4. In spreadsheets, use ISOWEEKNUM rather than WEEKNUM unless you specifically want the US convention, and say which one you used in the report footer.
5. State the convention explicitly in any shared document. "Week 12 (ISO)" removes an entire category of confusion for one extra word.

Frequently Asked Questions

Does the week start on Sunday or Monday? Both, depending on where you are. ISO 8601 and most of the world use Monday. The United States, Canada, Japan, Israel, India, and most of Latin America use Sunday.

Why does the US start the week on Sunday? It inherited the arrangement where the Sabbath is the seventh day, which makes the day after it the first. The convention predates the modern five-day working week and was never revised.

Which country starts the week on Friday? The Maldives, and only the Maldives. It is the sole territory in the Unicode CLDR dataset with a Friday firstDay value.

Is Sunday the first or last day of the week? Under ISO 8601 it is the seventh and last day. Under the US convention it is the first. Both are correct within their own system.

Do all Middle Eastern countries start the week on Saturday? No. Fourteen countries do, including Egypt, Iraq, and Qatar. But Saudi Arabia and Yemen start on Sunday, and the UAE and Lebanon start on Monday.

Which country is Monday-first? Most of them. Roughly 78 territories are explicitly listed as Monday-first, and every territory without an explicit entry defaults to Monday.