ISO week reference
Week 1 2026: December 29, 2025 – January 4, 2026
Exact Monday-to-Sunday dates for 2026-W01. Use this week as a calendar reference, open it in the planner, or view it in the full 2026 ISO calendar.
Week1
ISO year2026
Weekdays5
QuarterQ4
ISO reference2026-W01
Starts
Ends
Length7 days
Exact dates
Dates in week 1
ISO weeks run Monday through Sunday.
MonDec 292025
TueDec 302025
WedDec 312025
ThuJan 12026
FriJan 22026
SatJan 32026
SunJan 42026
Use this week
Open Week 1 Planner
Turn these dates into a plan
Open a private weekly planner already set to December 29, 2025 – January 4, 2026, then add priorities, deadlines, meetings and hourly work blocks.