What week of the year is October 1, 2026?

Week 40

ISO week of 2026

Sep 28 – Oct 4, 2026

Week details

W40ISO week
Sep 28week starts (Mon)
Oct 4week ends (Sun)
53weeks in 2026
1stweek of the month
Q4quarter
Thursdayweekday
7days since week started

Which week is it?

Thursday, October 1, 2026 falls in ISO week 40 of 2026. That week runs from Monday Monday, September 28, 2026 to Sunday Sunday, October 4, 2026, and it touches September and October. The ISO year 2026 has 53 weeks in total, so this is week 40 of 53, or about 75% of the way through the ISO year.

How ISO week numbers work

ISO 8601 weeks begin on Monday, and week 1 is the week that contains the first Thursday of the year. Because of that rule, the first days of January can belong to the last week of the previous year and the last days of December can belong to week 1 of the next. Most years have 52 weeks; roughly every five or six years a 53rd week is added to keep the count aligned with the seasons.

Planning by week

Schedules in manufacturing, logistics, education and project management are often written in week numbers, for example a delivery in week 40 or a sprint that ends in week 42. The week began 7 days ago. Keep in mind that US calendars often start the week on Sunday and use a different rule for week 1, so week numbers can differ between countries.

Nearby weeks

The week before is week 39, and the week after is week 41. The year pages list every week with its date range, and the week-number pages link to each of them.

Frequently asked questions

What week number is October 1, 2026?

ISO week 40 of 2026.

When does week 40 of 2026 start?

On Monday, Monday, September 28, 2026.

When does week 40 of 2026 end?

On Sunday, Sunday, October 4, 2026.

How many weeks are in 2026?

53 ISO weeks.

Which day starts the ISO week?

Monday.

What defines week 1?

The week containing the first Thursday of the year.

Can a date in January belong to the previous year's week?

Yes, when January 1 to 3 fall before the first Thursday.

What week of the month is it?

The 1st week of the month, counting by seven-day blocks from the 1st.

RESULT & PLANNING

Use this calculation

What Week Is October 1, 2026?: Week 40 ISO week of 2026 — Sep 28 – Oct 4, 2026

How this calculation was worked out

The result uses the exact inputs on this page and calendar/time arithmetic appropriate to this calculator. The result shown above is the value to use for this calculation.

Working days and weekends

4Calendar days
2Weekdays
1Saturdays
1Sundays
Not included unless this calculator says otherwisePublic holidays

Practical planning milestones

  1. Calculated dateThursday, October 1, 2026

Accuracy and limitations

  • The result uses the calendar rules and time zone shown on this page.
  • Leap years and actual month lengths are handled by the calendar arithmetic where they affect the calculation.

Save or share this result

Calculation history

Machine-readable result
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