Samsung
Show or Hide Calendar Week Numbers auf Samsung
Samsung Calendar hides week numbers by default. The month and week views only show day and date, which forces anyone working with ISO week numbers for invoicing, shift plans, or project deadlines to count manually from the start of the year.
The toggle for this feature is not part of the general phone settings. It lives inside the calendar app menu itself, which is why many people never find it. Open Tap on Calendar ➔ Open the Menu ➔ Tap on Settings ➔ Enable or disable Show week numbers to switch it on or off.
Once enabled, the current week number appears in a thin column on the left edge of the month and week views. This is a purely visual change: it does not affect event sync, reminders, or how dates are stored.
If you are looking for week numbers in a home screen widget or a different app, this setting will not help, since it only controls the built-in Samsung Calendar view.