Reminder of ISO weeks, which may give you a different 'year value' than regular weeks/days:

* https://en.wikipedia.org/wiki/ISO_week_date

* https://isoweeks.com

2025-12-29 will be 2026-W01-1:

* https://www.webcal.guru/en-CA/event_list/system_iso_week

* https://calendar.online/calendar-weeks/2026