JavaScript, PHP and various other web-based languages have date functions whose weeks begin on Sunday and end on Saturday. That is, as individual days, Sunday is identified 0 and Saturday is 6 (with Monday to Friday in between). Logically then, a calendar should start on Sunday and end on Saturday

However, a lot of calendars begin their weeks on Monday. Google's Calendar being one of them.

Does it matter at all from a user experience perspective what day I start my calendar on?
Would users expect to be able to switch between Sunday and Monday as the start of a week?

  • 1
    What is your calendar going to be used for?
    – JonW
    Oct 9, 2013 at 14:34
  • 7
    Isn't this a matter of localization? According to the ISO standard, Monday is the beginning of the week (see: en.wikipedia.org/wiki/ISO_week_date).
    – cimmanon
    Oct 9, 2013 at 14:46
  • 1
    I'm more referring to what sort of events are going to be displayed really. For instance if it's a calendar reflecting football matches that primarily occur on a Saturday then a different start day is possibly preferable compared to if it's a calendar reflecting weekday meetings.
    – JonW
    Oct 9, 2013 at 14:46
  • 3
    If it's being used in a corporate setting then it does matter. Large companies run in terms of their financial year, and their fincanial calendar will define if weeks begin on Sundays or Mondays. This choice will permeate through all their internal systems and spreadsheets, and will be the defacto default that the users will expect.
    – Racheet
    Oct 9, 2013 at 14:55
  • 2
    My calendar starts on a Wednesday. That way I have 3 days at work, then 2 days off for Saturday and Sunday, then I'm back to work for 2 days and then it's the weekend!
    – JonW
    Oct 9, 2013 at 15:11

4 Answers 4


Yes, it matters (especially in parts of the world where week numbers are important).

There are three main calendar formats defining the starting day of the week; Monday (used by most of Europe and the rest of the world that adheres to ISO-8601), Saturday (used by much of the Middle East), and Sunday (used in North America and Israel):

Image showing the first day of the week on a map, with Sunday in blue, Monday in yellow and Saturday in green
Image from Wikipedia

In the above map, countries shown in blue start their week on Sunday, in yellow on Monday and in lime green on Saturday.

  • Linux command line: locale first_weekday which returns 1 for Sunday, 2 for Monday etc. Mar 9, 2018 at 13:16

Yes, it matters, but which day you choose as the first day of the week depends on the use of the calendar.

  • If you work at a large company, there may be standards that you should follow.
  • Most "general use" calendars start the day of the week on Sunday
  • However, there are many specific applications that wouldn't make sense with Sunday being the first day of the week. For example, if you are creating a calendar for tracking weekend plans, having Saturday and Sunday be parts of different weeks wouldn't make sense.

Here's how I would answer the question:

  • Unless you have a very good reason not to, your calendar week should start on Sunday or Monday
  • You should default to Sunday, unless your application is tracking events that would make sense grouped together on both weekend days
  • Similarly, if this is going to be a work-related calendar in which the first day of the work week is Monday, then it makes sense to treat the weekend as "last week's weekend", not Saturday of last week and Sunday of this week.

User settings are fine, and will solve most of the problem, but I avoid user settings unless they are absolutely necessary. In most cases, you can go with a default that makes sense and satisfy 90% of the users.

  • 9
    Only most "general use" calendars developed in the US. Most general use calendars developed in Europe start the week on Monday. Oct 10, 2013 at 6:29
  • With something like this, I'd say a user setting is actually really important. Your default might cover 90% of users, but for the 10% who it doesn't cover, it's likely to really annoy.
    – Racheet
    Oct 10, 2013 at 9:18
  • 1
    Good points, both. My assumptions are US centric.
    – Jeremy T
    Oct 10, 2013 at 14:29

You can decide yourself whether it matters or not: use a calendar with different week beginning day only for a month. Write all your appointments, meetings into it. It's a huge pain!

Hungarian name for Monday is hétfő (spelled as cca. "hate-foe"), which means literally "week head". If this information appears even in the day's name, you may imagine how important it is.

You should offer a default, but let user choose it. You should't find out it from locale or language, maybe it's a mixed situation: say, an American company (Sunday) in a Central-European region (Monday).

I'm using Windows Phone 8 (#challengeaccepted), and I couldn't set language to English and week begin to Monday. Fortunately, calendar locale can be selected separately from system locale, so my phone now talks English, except week names, they appear Hungarian. But I'm happy with it, as it's the only way to set week beginning to hétfő.

  • I hate it when the regional settings are coupled with the language like that! You should be able to define each separately. Oct 11, 2013 at 1:39

In different countries the week starts on different days and the work week consists of different days.

If your calendar is to be used internationally, you must enable users to select the beginning of the week day and the work days/weekend days.

Also, if you enable location dependant defaults, users will have less work to do.

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