the week numbering can only be correct when set to ISO 8601 on MacOS, but on my phone the week numbering is still incorrect, and there is NO option for ISO 8601.
this is extremely frustrating. the calendar is synced between my devices, but the week numbering are not.
can Apple fix this on iOS? this is such an simple, low-level, and significant international standard thing.
MacBook Pro 14″, macOS 15.3
> iOS 18’s Calendar DOES appear to line-up w/ ISO 8601 (at least for 2025)
2025 is not affected by this misalignment of week numbering;
a 53-week year only happens once a couple of years.
compare ISO 8601 with iOS Apple Calendar for the year 2026 and 2027 as examples and you will see.
> After a bit of research on the subject
research more before suggesting that this is not an issue
> If all of your Apple devices are using the same Gregorian, is that not sufficient ?
it is not sufficient.
i look at the week number very frequently - work and archives are organised around weeks.
it doesn't make sense and causes confusion when you have a week number on one device that is correct and is aligned with international standard, and another week number on another device that is off by 1 week.
is this clear?
Workaround: Use the Gregorian calendar with “Start Week” on Monday.
This will produce week numbers which accurately correlate with ISO numbering thru 27 Dec 2026. (2026-w52-d7)
After that point, Gregorian rolls to week-1 while ISO continues to week-53.
(As 2027-01-01 occurs on a Friday)
Most of the world uses ISO 8601 week numbering. The US does not.
Would it be nice to have the option of selecting the week-numbering used, much as Celsius and Metric? Sure.
Why? Converting too and from different systems is always an issue, and always a source of errors.
Current (least bad) workaround? Set your region to one that has your preferred calendar week numbering.
Log feedback: https://apple.com/feedback
For some previous discussions, search for “week numbering” Apple iPhone or similar.
ChatGPT says:
The ISO 8601 standard defines the first week of the year as the one containing the first Thursday, ensuring each week starts on Monday. This system may result in years having either 52 or 53 weeks. In contrast, some regional systems, such as the U.S. week numbering system, start weeks on Sunday, leading to potential discrepancies in week numbering between these systems.
Year 2026:
In 2026, both systems align, with Week 1 commencing in the final days of 2025 and Week 53 occurring at the end of 2026.
Year 2027:
In 2027, the systems diverge: ISO 8601 designates 52 weeks starting in January, while the U.S. system assigns 53 weeks beginning in late December 2026.
These differences highlight how varying week numbering conventions can lead to misalignments, particularly in years where the number of weeks differs between systems.
After a bit of research on the subject:
If the iPhone app is set to Gregorian w/ the week starting on Monday …
… iOS 18’s Calendar DOES appear to line-up w/ ISO 8601 (at least for 2025)
Specifically:
2025-01-01 displays as Wk 1, Day 3
2025-02-28 displays as Wk 9, Day 5
2025-12-28 displays as Wk 52, Day 7
Jan 2025 calendar image attached:
While not an answer … I’m curious how does this “inability” impact you ?
If all of your Apple devices are using the same Gregorian, is that not sufficient ?
Are you encountering issues with certain apps or in collaborating with other users ?
thanks for adding context to this thread.
this creates confusion and potential misunderstanding in work involving planing and record keeping.
i was quite surprised to see that Apple has this inconsistency across OSs.
Re: “… is this clear? …”
It never was “Not Clear”
Nor did I ever claim that it was not an issue.
And it WILL indeed introduce errors (The very thing that “standards” are developed to reduce if not completely eliminate)
2026 is indeed a 53 week year … and the iOS workaround provided will work thru the week ending 2026-12-27. (2026-w52)
With any luck at all Apple might provide a permanent iOS solution — especially given that they already have it in MacOS; something which I’m confident that you pointed-out via your Feedback — in the 95-weeks remaining ‘till then. 🤞
thanks. i just did, following your link.
Furthermore … I’ve provided Feedback as well; as I too agree that it IS an item worthy of Apple’s attention.
ok, i guess i misread your tone; maybe because of how you emphasise your words. i don't know
> the iOS workaround provided
what is this workaround? is there one?
Week Numbering Incorrect; ISO 8601 Calendar Needs To Be Added To iOS
