Monday or Sunday start

There is no correct answer, but there is a correct source, and a lot of what is written about this is wrong.

What the data says

Unicode CLDR is the authoritative machine-readable source for locale conventions, and it is what operating systems and browsers actually use. Its world default is Monday. By territory:

Sunday: United States, India, Canada, Australia, Japan, China, Brazil, South Africa, Israel, Mexico, Pakistan, the Philippines, Singapore, Hong Kong, South Korea

Monday: United Kingdom, Ireland, New Zealand, Germany, France, and most of Europe

Saturday: United Arab Emirates, Egypt and much of the Gulf

Three of these contradict things commonly repeated online and are worth flagging:

India is Sunday-start. Several widely-cited sources claim Monday. CLDR says Sunday.

Australia is Sunday but New Zealand is Monday. They cannot share a default, which surprises people who assume the two follow each other.

Ireland only moved to Monday in CLDR release 34. It was Sunday historically, so older software and stale data still return Sunday for Ireland.

What ISO 8601 says

ISO 8601 is unambiguous: Monday is day one, Sunday is day seven.

That matters beyond preference, because it decides whether week numbers are meaningful. ISO week one is the week containing the first Thursday of the year, equivalently the week containing 4 January. Weeks run Monday to Sunday, and each week belongs to the year its Thursday falls in, which is why late December can be week one of the following year.

ISO week numbers are only defined for Monday-start weeks. The US convention of week one containing 1 January is a genuinely different algorithm and produces different numbers for the same days. Printing one and labelling it as the other is worse than leaving the number off, which is why our Sunday-start files do not show one.

Week numbering is native business vocabulary in the Nordics, Germany, France, Spain and Italy, where people say week 35 the way others say late August. It is largely unfamiliar in the US.

The two real arguments

Beyond convention, planner users make two arguments and both are reasonable.

For Monday: the weekend stays together. On a Sunday-start week, Saturday and Sunday sit at opposite ends of the row, and if you plan the weekend as one thing it is split across the page.

For Sunday: some people’s working week genuinely starts on Sunday. Church staff, Sunday-to-Thursday schedules, and the Gulf and Israeli working pattern.

If neither applies, use your country’s convention. It is what the shared calendars you interact with will assume.

The complaint that actually matters

The loudest thing planner users say about week start is not about which day. It is about inconsistency.

Commercial planners routinely print a month grid running Sunday to Saturday and a week view running Monday to Sunday, in the same book. It makes the mini-month useless as a reference for the week view, because the columns do not line up.

It is a real defect and an easy one to avoid. Week start on this site is a single global setting that propagates to every artifact in a download: the week grid, every mini-month, the month overviews and the year index. There is an automated test asserting the mini-month’s first column matches the grid’s, because it is exactly the sort of thing that drifts.

The weekend compression option

If you use a Sunday start and the split weekend bothers you, there is a standard commercial fix: put Saturday and Sunday in one column, divided into two half-height cells.

It also buys width. On landscape Letter, six columns instead of seven gives 39.8 mm per day rather than 34.1 mm, which lands exactly on the industry-standard 38.1 mm day width.

Saturday start

Genuinely used across the Gulf and in Israel, where the working week runs Sunday to Thursday. It is offered here as a real option rather than an edge case, because for those readers the alternatives put the weekend in the middle of the page.

What your software already thinks

Most operating systems and browsers derive the week start from your locale, using the same CLDR data described above. If you have never changed it, your phone’s calendar is already showing you your region’s convention.

That is worth checking before choosing, because a paper planner that disagrees with the calendar you look at daily creates friction every time you transfer something between them.

You can override it in most systems, and if you do, override it everywhere rather than in one place.

Switching

If you want to change, switch everything at once and give it a month. The first fortnight will feel wrong regardless of which direction you are going, because reading a week is a pattern-recognition task and the pattern has moved.

Do not run one system on paper and another on screen while you decide. That is the arrangement that produces mistakes.

Five-day weeks

If your planner is for work or study rather than life, a five-day sheet sidesteps the question. Monday to Friday reads the same in either convention, and the columns are noticeably wider: on landscape Letter, five columns give about 47 mm each against 34 mm for seven.

Class timetables and shift rotas are almost always better as five-day sheets for this reason.

What we do

Week start is a single global setting that propagates to every artifact in a download: the week grid, every mini-month, the month overviews and the year index. There is an automated test asserting the mini-month’s first column matches the grid’s.

The default is derived from your browser’s locale on your first visit, and once you choose explicitly, that choice is remembered and geography never overrides it again.