I noticed that many "month calendars/date pickers" start with Sunday and end with Saturday in the header - Is this a standard in the western world or is it a convention or is there any reason behind this?

Example of what I am referring to.


3 Answers 3


According to the International Organization for Standardization, Monday is considered the first day of the week.

ISO 8601:

The ISO week-numbering year starts at the first day (Monday) of week 01 and ends at the Sunday before the new ISO year (hence without overlap or gap). It consists of 52 or 53 full weeks.

That being said, I do not have an answer as to why so many datepickers have a Sunday default week start.

  • Thank you for your answer. The ISO is a good point.
    – NoChance
    Nov 5, 2018 at 15:25
  • Despite the ISO's standard, in the US users expect a Su -> Sa model as default. Most business-oriented solutions (and many consumer) also provide a setting for Mo -> Su. Nov 5, 2018 at 18:18
  • @plainclothes I've run into this alot because I work on b2b apps. Every time, the first thing that's requested is how to tweak the datepicker to a Mon > Sun layout.
    – Mike M
    Nov 5, 2018 at 18:21
  • Been there too. Then I tracked the usage and found that the vast majority of users ended up changing it back to Su -> Sa within the first week. The most used calendar customization was hiding the weekend altogether 🙃 Nov 6, 2018 at 0:15

In the US, the standard week is considered to start on Sunday. So calendar pickers created using the US standard will follow the same convention. I believe many pickers can be changed so the week starts on Monday, but if the web designer is also from the US, I wouldn't expect them to add that option.

  • Thank you for your answer and it is correct. I had to designate the other entry because I found the reference to ISO helpful in my case. Thanks again.
    – NoChance
    Nov 5, 2018 at 15:25

Although ISO define Monday as the first day of the week, there are cultural differences. According to First Day of the Week in Different Countries at ChartsBin.com – which shows a nice map of the world as well as listing the first day of the week for 108 countries – the world divides into three categories:

  • Monday: 61 countries, predominately Europe, Russia, India, S.E. Asia and Australia.

  • Sunday: 32 countries, predominately USA, Canada, most of South America, China and Japan.

  • Saturday: 15 countries, predominately North Africa and the Middle East.

Note: The chart does not show any preference for most of the countries in Africa.

Although as pboss3010 says in their answer, if most date-pickers start with Sunday, it was probably because the first data-pickers were written by, or for, the US market (and/or before internationalisation was "a thing").

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