Week number calculator
The ISO week number counts weeks that start on Monday, and week 1 is the week that holds the year's first Thursday. October 11, 2026 falls in week 41.
October 11, 2026 is in ISO week
41 of 2026
- Week-numbering year
- 2026
- Weeks in that year
- 53
- Week starts (Monday)
- Oct 5, 2026
- Week ends (Sunday)
- Oct 11, 2026
Calendar of 2026 with ISO week numbers
January
| Wk | M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|---|
| 1 | 1 | 2 | 3 | 4 | |||
| 2 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
| 3 | 12 | 13 | 14 | 15 | 16 | 17 | 18 |
| 4 | 19 | 20 | 21 | 22 | 23 | 24 | 25 |
| 5 | 26 | 27 | 28 | 29 | 30 | 31 |
February
| Wk | M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|---|
| 5 | 1 | ||||||
| 6 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| 7 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
| 8 | 16 | 17 | 18 | 19 | 20 | 21 | 22 |
| 9 | 23 | 24 | 25 | 26 | 27 | 28 |
March
| Wk | M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|---|
| 9 | 1 | ||||||
| 10 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| 11 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
| 12 | 16 | 17 | 18 | 19 | 20 | 21 | 22 |
| 13 | 23 | 24 | 25 | 26 | 27 | 28 | 29 |
| 14 | 30 | 31 |
April
| Wk | M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|---|
| 14 | 1 | 2 | 3 | 4 | 5 | ||
| 15 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| 16 | 13 | 14 | 15 | 16 | 17 | 18 | 19 |
| 17 | 20 | 21 | 22 | 23 | 24 | 25 | 26 |
| 18 | 27 | 28 | 29 | 30 |
May
| Wk | M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|---|
| 18 | 1 | 2 | 3 | ||||
| 19 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| 20 | 11 | 12 | 13 | 14 | 15 | 16 | 17 |
| 21 | 18 | 19 | 20 | 21 | 22 | 23 | 24 |
| 22 | 25 | 26 | 27 | 28 | 29 | 30 | 31 |
June
| Wk | M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|---|
| 23 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| 24 | 8 | 9 | 10 | 11 | 12 | 13 | 14 |
| 25 | 15 | 16 | 17 | 18 | 19 | 20 | 21 |
| 26 | 22 | 23 | 24 | 25 | 26 | 27 | 28 |
| 27 | 29 | 30 |
July
| Wk | M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|---|
| 27 | 1 | 2 | 3 | 4 | 5 | ||
| 28 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| 29 | 13 | 14 | 15 | 16 | 17 | 18 | 19 |
| 30 | 20 | 21 | 22 | 23 | 24 | 25 | 26 |
| 31 | 27 | 28 | 29 | 30 | 31 |
August
| Wk | M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|---|
| 31 | 1 | 2 | |||||
| 32 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| 33 | 10 | 11 | 12 | 13 | 14 | 15 | 16 |
| 34 | 17 | 18 | 19 | 20 | 21 | 22 | 23 |
| 35 | 24 | 25 | 26 | 27 | 28 | 29 | 30 |
| 36 | 31 |
September
| Wk | M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|---|
| 36 | 1 | 2 | 3 | 4 | 5 | 6 | |
| 37 | 7 | 8 | 9 | 10 | 11 | 12 | 13 |
| 38 | 14 | 15 | 16 | 17 | 18 | 19 | 20 |
| 39 | 21 | 22 | 23 | 24 | 25 | 26 | 27 |
| 40 | 28 | 29 | 30 |
October
| Wk | M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|---|
| 40 | 1 | 2 | 3 | 4 | |||
| 41 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
| 42 | 12 | 13 | 14 | 15 | 16 | 17 | 18 |
| 43 | 19 | 20 | 21 | 22 | 23 | 24 | 25 |
| 44 | 26 | 27 | 28 | 29 | 30 | 31 |
November
| Wk | M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|---|
| 44 | 1 | ||||||
| 45 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| 46 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
| 47 | 16 | 17 | 18 | 19 | 20 | 21 | 22 |
| 48 | 23 | 24 | 25 | 26 | 27 | 28 | 29 |
| 49 | 30 |
December
| Wk | M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|---|
| 49 | 1 | 2 | 3 | 4 | 5 | 6 | |
| 50 | 7 | 8 | 9 | 10 | 11 | 12 | 13 |
| 51 | 14 | 15 | 16 | 17 | 18 | 19 | 20 |
| 52 | 21 | 22 | 23 | 24 | 25 | 26 | 27 |
| 53 | 28 | 29 | 30 | 31 |
When week 1 starts, year by year
Week 1 always contains January 4, and every ISO week starts on a Monday. That makes the first Monday of the numbering year fall anywhere from December 29 to January 4.
A year has 53 weeks when January 1 is a Thursday, or a Wednesday in a leap year. Otherwise it has 52.
| Year | Week 1 starts (Monday) | Weeks in the year |
|---|---|---|
| 2025 | Dec 30, 2024 | 52 |
| 2026 | Dec 29, 2025 | 53 |
| 2027 | Jan 4, 2027 | 52 |
| 2028 | Jan 3, 2028 | 52 |
| 2029 | Jan 1, 2029 | 52 |
| 2030 | Dec 31, 2029 | 52 |
How are ISO week numbers counted?
ISO 8601 weeks run from Monday to Sunday. Week 1 of a year is the week that contains its first Thursday, which is the same as the week containing January 4. The calculator finds the Thursday of the week your date is in, takes the year of that Thursday and counts the weeks since its January 1.
Why can January 1 be in week 52 or 53?
Because a week belongs to the year that holds most of it. January 1, 2027 is a Friday, so it sits in the last week of 2026, week 53. Week 1 of 2027 starts on Monday, January 4, 2027. In the same way, Monday, December 29, 2025 already belongs to week 1 of 2026.
Which years have 53 weeks?
A year has 53 ISO weeks when January 1 is a Thursday, or a Wednesday in a leap year. In the next two decades that is 2026, 2032, 2037, 2043. All other years have 52 weeks. The year calendar under the calculator shows the week number beside every row of days.
Is the ISO week the same as the week number in my calendar app?
Not always. Some calendars start weeks on Sunday and call the week with January 1 week 1, which can differ from the ISO number by one around the turn of the year. If a deadline says "week 41", check which numbering it uses; this page gives the ISO one.
Questions about week number
What week number is it today?
The calculator opens on today's date and shows the week at once, with the Monday it starts and the Sunday it ends.
How many weeks are in a year?
Either 52 or 53 ISO weeks. 2026 has 53, so the week that contains January 1, 2027 is still counted as the last week of 2026.
When does week 1 of 2027 start?
On Monday, January 4, 2027, because the first Thursday of 2027 is January 7.
Is the week number the same as the week of the month?
No. ISO week numbers count from the start of the year, from 1 to 52 or 53, and ignore months.
Does the first day of the week change the number?
In ISO 8601 the week always starts on Monday. The calendar below shows Monday first so the rows match the numbers.
Related tools
Other ways to count with dates.
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What date is 90 days from now? Days, weeks, months or years.Business days
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Christmas, Thanksgiving, Easter and eight more.
Sources and limits
- ISO 8601 week date (open description)
Weeks start on Monday and week 1 is the week with the year’s first Thursday. The standard itself is sold by ISO and could not be opened, so this is an open description, not the normative text.
Wikipedia (secondary source). Opened on .
Not confirmed: The ISO 8601 standard is sold by ISO and its page could not be opened, so the week rule here comes from an open description and is checked against .NET’s ISOWeek class in the tests, not against the standard’s own text.
This is a calculation aid. For payroll, contracts, court deadlines, visas or tax dates, confirm the count with the official calendar of the organisation that sets the deadline. Nothing you type leaves your browser.