First, go to Settings > Calendar to set Week Numbers > On and Start Week On > (any weekday you like). Now the Calendar app will rearrange the week layout for you.
Let’s confirm this:
| Start Week On | the Calendar Layout |
|---|---|
| Monday | Monday Tuesday Wednesday Thursday Friday Saturday Sunday |
| Tuesday | Tuesday Wednesday Thursday Friday Saturday Sunday Monday |
| Wednesday | Wednesday Thursday Friday Saturday Sunday Monday Tuesday |
| Thursday | Thursday Friday Saturday Sunday Monday Tuesday Wednesday |
| Friday | Friday Saturday Sunday Monday Tuesday Wednesday Thursday |
| Saturday | Saturday Sunday Monday Tuesday Wednesday Thursday Friday |
| Sunday | Sunday Monday Tuesday Wednesday Thursday Friday Saturday |
Second, now pay attention to the middle day of the week layout.
Let’s confirm this:
| Start Week On | the Middle Day of Current Week Layout (in Bold) |
|---|---|
| Monday | Monday Tuesday Wednesday 4th: Thursday Friday Saturday Sunday |
| Tuesday | Tuesday Wednesday Thursday 4th: Friday Saturday Sunday Monday |
| Wednesday | Wednesday Thursday Friday 4th: Saturday Sunday Monday Tuesday |
| Thursday | Thursday Friday Saturday 4th: Sunday Monday Tuesday Wednesday |
| Friday | Friday Saturday Sunday 4th: Monday Tuesday Wednesday Thursday |
| Saturday | Saturday Sunday Monday 4th: Tuesday Wednesday Thursday Friday |
| Sunday | Sunday Monday Tuesday 4th: Wednesday Thursday Friday Saturday |
Third, choose a year which its January 1st is the middle day of the current week layout and you will get a wrong(?) week number.
Let’s confirm this:
| Start Week On | Middle Day | Check These Years | Display as |
|---|---|---|---|
| Monday | 4th: Thursday | 2015, 2026, 2032 | Week #53: Dec 29, Dec 30, Dec 31, Jan 01, Jan 02, Jan 03, Jan 04 |
| Tuesday | 4th: Friday | 2010, 2016, 2021, 2027 | Week #53: Dec 29, Dec 30, Dec 31, Jan 01, Jan 02, Jan 03, Jan 04 |
| Wednesday | 4th: Saturday | 2011, 2022, 2028, 2033 | Week #53: Dec 29, Dec 30, Dec 31, Jan 01, Jan 02, Jan 03, Jan 04 |
| Thursday | 4th: Sunday | 2012, 2017, 2023, 2034 | Week #53: Dec 29, Dec 30, Dec 31, Jan 01, Jan 02, Jan 03, Jan 04 |
| Friday | 4th: Monday | 2018, 2024, 2029, 2035 | Week #53: Dec 29, Dec 30, Dec 31, Jan 01, Jan 02, Jan 03, Jan 04 |
| Saturday | 4th: Tuesday | 2013, 2019, 2030 | Week #53: Dec 29, Dec 30, Dec 31, Jan 01, Jan 02, Jan 03, Jan 04 |
| Sunday | 4th: Wednesday | 2014, 2020, 2025, 2031 | Week #53: Dec 29, Dec 30, Dec 31, Jan 01, Jan 02, Jan 03, Jan 04 |
Here is my concern, take Start Week On > Monday as example.
Let’s confirm this:
| Combination (Mon Tue Wed Thu Fri Sat Sun) | iOS Calendar | ISO code 8601 |
|---|---|---|
| Dec 26, Dec 27, Dec 28, Dec 29, Dec 30, Dec 31, Jan 01 | Week #53 | Week #53 |
| Dec 27, Dec 28, Dec 29, Dec 30, Dec 31, Jan 01, Jan 02 | Week #53 | Week #53 |
| Dec 28, Dec 29, Dec 30, Dec 31, Jan 01, Jan 02, Jan 03 | Week #53 | Week #53 |
| Dec 29, Dec 30, Dec 31, Jan 01, Jan 02, Jan 03, Jan 04 | Week #53 <– (?) | Week #01 |
| Dec 30, Dec 31, Jan 01, Jan 02, Jan 03, Jan 04, Jan 05 | Week #01 | Week #01 |
| Dec 31, Jan 01, Jan 02, Jan 03, Jan 04, Jan 05, Jan 06 | Week #01 | Week #01 |
| Jan 01, Jan 02, Jan 03, Jan 04, Jan 05, Jan 06, Jan 07 | Week #01 | Week #01 |
Is this a bug of the iOS app Calendar or just some special rules that it follows which I didn’t know before?
