Is there a way to have Calendar.app display its week numbers using the standard ISO 8061 week definition?
The standard says a week starts on Monday, and the first Thursday of the year defines the first week. So at the end of 2015, the standard week of 2015-12-28 to 2016-01-03 is Week 53
. In contrast, Calendar.app in Yosemite & Mountain Lion shows Week 1
.
I'm wondering:
- What definition of week is Apple using? Perhaps simply the First of January is always Week 1?
- Is there any way to change this default behavior to show standard weeks?
Best Answer
Calendar System
System Preferences in Yosemite 10.10.5 (and all later OS X releases, through El Capitan 10.11.3) lets you change the calendar system used across apps. The default for a United States install is
Gregorian
. To get behavior compliant with the ISO 8601 standard, change toISO 8601
.Choose
System Preferences > Language & Region > Calendar (popup menu) > ISO 8601
.Below are screen shots of Apple’s Calendar.app, before and after switching between Gregorian calendar and ISO 8601 calendar. I added the "Gregorian"/"ISO" labels.
Note the week numbers shown on the left. Weeks
52
&1
changed to weeks52
&53
. In a standard week, January 1st of 2016 is in Week 53. In ISO 8601 notation for weeks, that would be the week2015-W53
, and January 1st 2016 would be2015-W53-5
with the weekday number appended.For more info, see an entire Wikipedia article dedicated to ISO week date.
CAVEAT I do not know the ramifications of changing your Mac calendar system from
Gregorian
toISO 8601
. I searched support.apple.com but found no documentation.