Week 1, 2026
December 29, 2025 – January 4, 2026
Monday December 29 – Sunday January 42026-W01Days 363–4 (365 → 1)
The seven days
| Date | ISO week date | Day of year | US week | Islamic date (computed) | Holidays and other dates |
|---|---|---|---|---|---|
| Mon, Dec 29, 2025 | 2026-W01-1 | 363 | 53 | 9 Rajab 1447 AH | |
| Tue, Dec 30, 2025 | 2026-W01-2 | 364 | 53 | 10 Rajab 1447 AH | |
| Wed, Dec 31, 2025 | 2026-W01-3 | 365 | 53 | 11 Rajab 1447 AH | New Year’s Eve |
| Thu, Jan 1 | 2026-W01-4 | 001 | 1 | 12 Rajab 1447 AH | New Year's Day (16 sets); The first day of January (Hong Kong) |
| Fri, Jan 2 | 2026-W01-5 | 002 | 1 | 13 Rajab 1447 AH | 2nd January (UK: Scotland); Day after New Year's Day (New Zealand) |
| Sat, Jan 3 | 2026-W01-6 | 003 | 1 | 14 Rajab 1447 AH | |
| Sun, Jan 4 | 2026-W01-7 | 004 | 2 | 15 Rajab 1447 AH |
About week 1
Week 1 straddles New Year: it begins in 2025 and ends in 2026, and under ISO 8601 all seven days belong to week 1 of 2026, even the days of December 2025. Week 1 is the week with the year’s first Thursday, here Thursday, January 1, 2026. In US numbering, where weeks start on Sunday and the week of January 1 is week 1, Monday to Wednesday are US week 53 of 2025, Thursday to Saturday US week 1 of 2026, and Sunday US week 2 of 2026.
Holidays this week: New Year's Day on Thu, Jan 1 in 16 of the countries and regions we cover; The first day of January on Thu, Jan 1 in Hong Kong; 2nd January on Fri, Jan 2 in UK: Scotland; Day after New Year's Day on Fri, Jan 2 in New Zealand. Also this week: New Year’s Eve on Wed, Dec 31 (December 31). All weeks of 2026 lists the neighbouring weeks.
Week 1 in other years
| Year | Week 1 runs |
|---|---|
| 2024 | Mon, Jan 1 – Sun, Jan 7 |
| 2025 | Mon, Dec 30 – Sun, Jan 5, 2025 |
| 2026 | Mon, Dec 29 – Sun, Jan 4, 2026 |
| 2027 | Mon, Jan 4 – Sun, Jan 10 |
| 2028 | Mon, Jan 3 – Sun, Jan 9 |
| 2029 | Mon, Jan 1 – Sun, Jan 7 |
In 2027, week 1 runs Mon, Jan 4 – Sun, Jan 10: 2026 has 53 weeks, so the same number comes 371 days later, 6 days later in the calendar. Over the 400-year cycle, the Monday of week 1 falls between December 29 and January 4.
By the end of week 1, 4 days of 2026 have passed (1.1% of the year), and 52 ISO weeks of 2026 remain. The week falls in Q4.
Writing week 1
ISO 8601 writes this week as 2026-W01 (basic format 2026W01), from 2026-W01-1 on Monday to -7 on Sunday. The week number page shows the spreadsheet and Python formulas that give these numbers.