Week 40 of 2026 runs September 28 to October 4

ISO week 40 of 2026 begins on Monday, September 28, 2026 and ends on Sunday, October 4, 2026. It starts in 5 days, about 1 week from the current week 39. The week covers the turn from September into October.

What dates are in week 40?

No holiday or widely marked observance falls inside week 40 of 2026. The seven dates always run Monday through Sunday, which is the part of ISO 8601 that most often catches people out: a week that starts on Sunday is a different convention and gives a different number.

How ISO week 40 is worked out

ISO 8601 fixes week one as the week containing the first Thursday of January, which is the same as saying the week containing 4 January, or the week holding the majority of its days in the new year. Counting forward from there, week 40 is the 40th Monday-to-Sunday block of 2026, which lands on September 28. All seven dates sit inside 2026, so the ISO year and the calendar year agree for this week.

When is week 40 in other years?

Week 40 shifts by a day or two each year because a year is 52 weeks plus one or two days, so the Monday that opens it moves from September 28 in 2026 to October 4 in 2027.

How far away is week 40?

Today is Wednesday, September 23, 2026, which sits in ISO week 39 of 2026. Week 40 of 2026 opens in 5 days, so there is roughly 1 week to go. Counting only complete weeks between now and then gives 0.

Questions

What dates are in week 40 of 2026?

Monday September 28, 2026 through Sunday October 4, 2026.

What week is it now?

ISO week 39 of 2026. Today is Wednesday, September 23, 2026.

How many weeks does 2026 have?

53. The 2026 week count page explains the rule.

Do ISO weeks start on Monday or Sunday?

Monday. A Sunday-first week is a different convention and can give a different week number for the same date.

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