ISO week 2026-W04

Week 4, 2026

Monday, January 19 – Sunday, January 25, 2026

ISO week 4 of 2026 (2026-W04) runs from Monday, January 19, 2026 to Sunday, January 25, 2026.

This week ended 38 weeks ago. The current week is week 42, 2026.

The 7 days of week 4

Dates in week 4, 2026
Day	Date	Day of year	US week	ISO date
Monday	January 19, 2026	19 of 365	4	2026-W04-1
Tuesday	January 20, 2026	20 of 365	4	2026-W04-2
Wednesday	January 21, 2026	21 of 365	4	2026-W04-3
Thursday	January 22, 2026	22 of 365	4	2026-W04-4
Friday	January 23, 2026	23 of 365	4	2026-W04-5
Saturday	January 24, 2026	24 of 365	4	2026-W04-6
Sunday	January 25, 2026	25 of 365	5	2026-W04-7

Week 4 at a glance

ISO code: 2026-W04 (Monday is 2026-W04-1, Sunday is 2026-W04-7)
Month: January
Quarter: Q1 of 2026
Day of year: Days 19–25 of 365
US week number: Monday–Saturday: US week 4; Sunday: US week 5 (Sunday-start weeks, week 1 contains January 1)
Even or odd: Week 4 is an even week
Weeks left: After this week, 49 ISO weeks remain in 2026 (53 weeks in total)
Year progress: By Sunday, 7% of 2026 has passed

Holidays and key dates

Monday, January 19: Martin Luther King Jr. Day – US federal holiday

Week numbers follow ISO 8601: weeks start on Monday and week 1 contains the first Thursday of the year. US weeks start on Sunday, with week 1 containing January 1.

Questions about week 4, 2026

What are the dates of week 4 in 2026?

Week 4 of 2026 starts on Monday, January 19, 2026 and ends on Sunday, January 25, 2026.

What month is week 4 of 2026?

Week 4 falls in January. By the Thursday rule that ISO 8601 uses for years and quarters, it counts as a January week.

How do I get week 4 of 2026 in Excel or Google Sheets?

=ISOWEEKNUM(DATE(2026,1,19)) returns 4. To go the other way, =DATE(2026,1,4)-WEEKDAY(DATE(2026,1,4),2)+1+(4-1)*7 returns the Monday, January 19, 2026.