ISO week 2026-W40

Week 40, 2026

Monday, September 28 – Sunday, October 4, 2026

ISO week 40 of 2026 (2026-W40) runs from Monday, September 28, 2026 to Sunday, October 4, 2026.

This week ended 2 weeks ago. The current week is week 42, 2026.

The 7 days of week 40

Dates in week 40, 2026
Day	Date	Day of year	US week	ISO date
Monday	September 28, 2026	271 of 365	40	2026-W40-1
Tuesday	September 29, 2026	272 of 365	40	2026-W40-2
Wednesday	September 30, 2026	273 of 365	40	2026-W40-3
Thursday	October 1, 2026	274 of 365	40	2026-W40-4
Friday	October 2, 2026	275 of 365	40	2026-W40-5
Saturday	October 3, 2026	276 of 365	40	2026-W40-6
Sunday	October 4, 2026	277 of 365	41	2026-W40-7

Week 40 at a glance

ISO code: 2026-W40 (Monday is 2026-W40-1, Sunday is 2026-W40-7)
Month: September and October
Quarter: Q4 by the ISO rule (its Thursday, October 1, is in Q4); the calendar dates span Q3 and Q4
Day of year: Days 271–277 of 365
US week number: Monday–Saturday: US week 40; Sunday: US week 41 (Sunday-start weeks, week 1 contains January 1)
Even or odd: Week 40 is an even week
Weeks left: After this week, 13 ISO weeks remain in 2026 (53 weeks in total)
Year progress: By Sunday, 76% of 2026 has passed

Holidays and key dates

Thursday, October 1: Q4 begins

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 40, 2026

What are the dates of week 40 in 2026?

Week 40 of 2026 starts on Monday, September 28, 2026 and ends on Sunday, October 4, 2026.

What month is week 40 of 2026?

Week 40 falls in September and October. By the Thursday rule that ISO 8601 uses for years and quarters, it counts as a October week.

How do I get week 40 of 2026 in Excel or Google Sheets?

=ISOWEEKNUM(DATE(2026,9,28)) returns 40. To go the other way, =DATE(2026,1,4)-WEEKDAY(DATE(2026,1,4),2)+1+(40-1)*7 returns the Monday, September 28, 2026.