ISO 8601
Weeks run Monday through Sunday. Week 1 contains the year's first Thursday, which is also the week containing January 4. A date near New Year can belong to the previous or next ISO year.
Current week number · Updated daily
What week is it?
It's week 42 of 2026
Monday, October 12 – Sunday, October 18, 2026
- Today is Tuesday, October 13, 2026 – day 286 of 365. 11 weeks left in 2026.
- ISO week 42 · US week (Sunday start): 42
- Even week · ISO code 2026-W42
- Based on UTC; your local time zone is used when JavaScript is available. Updated daily, last updated .
The year in weeks
ISO week numbers for 2026
All 53 weeks of 2026 with Monday, Sunday, month span and quarter. Select a week for its dates, holidays and US week number. The current week is highlighted.
| Week | ISO code | Monday | Sunday | Month | Quarter |
|---|---|---|---|---|---|
| 1 | 2026-W01 | Dec/Jan | Q1 | ||
| 2 | 2026-W02 | Jan | Q1 | ||
| 3 | 2026-W03 | Jan | Q1 | ||
| 4 | 2026-W04 | Jan | Q1 | ||
| 5 | 2026-W05 | Jan/Feb | Q1 | ||
| 6 | 2026-W06 | Feb | Q1 | ||
| 7 | 2026-W07 | Feb | Q1 | ||
| 8 | 2026-W08 | Feb | Q1 | ||
| 9 | 2026-W09 | Feb/Mar | Q1 | ||
| 10 | 2026-W10 | Mar | Q1 | ||
| 11 | 2026-W11 | Mar | Q1 | ||
| 12 | 2026-W12 | Mar | Q1 | ||
| 13 | 2026-W13 | Mar | Q1 | ||
| 14 | 2026-W14 | Mar/Apr | Q2 | ||
| 15 | 2026-W15 | Apr | Q2 | ||
| 16 | 2026-W16 | Apr | Q2 | ||
| 17 | 2026-W17 | Apr | Q2 | ||
| 18 | 2026-W18 | Apr/May | Q2 | ||
| 19 | 2026-W19 | May | Q2 | ||
| 20 | 2026-W20 | May | Q2 | ||
| 21 | 2026-W21 | May | Q2 | ||
| 22 | 2026-W22 | May | Q2 | ||
| 23 | 2026-W23 | Jun | Q2 | ||
| 24 | 2026-W24 | Jun | Q2 | ||
| 25 | 2026-W25 | Jun | Q2 | ||
| 26 | 2026-W26 | Jun | Q2 | ||
| 27 | 2026-W27 | Jun/Jul | Q3 | ||
| 28 | 2026-W28 | Jul | Q3 | ||
| 29 | 2026-W29 | Jul | Q3 | ||
| 30 | 2026-W30 | Jul | Q3 | ||
| 31 | 2026-W31 | Jul/Aug | Q3 | ||
| 32 | 2026-W32 | Aug | Q3 | ||
| 33 | 2026-W33 | Aug | Q3 | ||
| 34 | 2026-W34 | Aug | Q3 | ||
| 35 | 2026-W35 | Aug | Q3 | ||
| 36 | 2026-W36 | Aug/Sep | Q3 | ||
| 37 | 2026-W37 | Sep | Q3 | ||
| 38 | 2026-W38 | Sep | Q3 | ||
| 39 | 2026-W39 | Sep | Q3 | ||
| 40 | 2026-W40 | Sep/Oct | Q4 | ||
| 41 | 2026-W41 | Oct | Q4 | ||
| 42 | 2026-W42 | Oct | Q4 | ||
| 43 | 2026-W43 | Oct | Q4 | ||
| 44 | 2026-W44 | Oct/Nov | Q4 | ||
| 45 | 2026-W45 | Nov | Q4 | ||
| 46 | 2026-W46 | Nov | Q4 | ||
| 47 | 2026-W47 | Nov | Q4 | ||
| 48 | 2026-W48 | Nov | Q4 | ||
| 49 | 2026-W49 | Nov/Dec | Q4 | ||
| 50 | 2026-W50 | Dec | Q4 | ||
| 51 | 2026-W51 | Dec | Q4 | ||
| 52 | 2026-W52 | Dec | Q4 | ||
| 53 | 2026-W53 | Dec/Jan | Q4 |
What week of the year is it?
Today is in week 42 of 53 in the ISO week-numbering year 2026. 11 weeks remain after this one. ISO 8601 weeks start on Monday and are the standard in Europe, much of Asia and international business.
Many US calendars, and Excel's default WEEKNUM, start weeks on Sunday and count the week containing January 1 as week 1. By that rule, today is in US week 42.
Numbering systems
ISO weeks and US week numbers
ISO 8601 gives one consistent answer internationally. US calendars and software may use different start days and a different rule for week 1.
Common US systems
Many US calendars start the week on Sunday and treat the week containing January 1 as week 1. Excel's WEEKNUM supports several return types, so results can differ from ISOWEEKNUM.
Two rules worth knowing
Week 1 and week 53
How is week 1 chosen?
ISO week 1 is the week with the first Thursday of the calendar year. Equivalently, it is the week containing January 4. That week can begin in December.
When does week 53 occur?
An ISO year has 53 weeks when January 1 is a Thursday, or when a leap year starts on Wednesday. See how many weeks are in a year for every year from 2020 to 2035.
Source: ISO's overview of ISO 8601. See our calculation methodology and tests for implementation details.
Quick answers
How many weeks are in 2026?
2026 has 53 ISO weeks, because January 1, 2026 is a Thursday. Week 1 runs Monday, December 29, 2025 – Sunday, January 4, 2026, and week 53 runs Monday, December 28, 2026 – Sunday, January 3, 2027.
What week number is it today?
Today, Tuesday, October 13, 2026, is ISO week 42 of 2026 (2026-W42). The week runs Monday, October 12 – Sunday, October 18, 2026. In the US system with Sunday-start weeks it is week 42.
When does week 1 start?
ISO week 1 is the week that contains the first Thursday of January, which is also the week containing January 4. Weeks start on Monday, so week 1 can begin as early as December 29 or as late as January 4. Week 1 of 2026 started on Monday, December 29, 2025.
Is this week an even or odd week?
Week 42 is an even week. Next week, week 43, is odd.
Why do Outlook or Excel show a different week number?
Outlook counts the week containing January 1 as week 1 by default, and Excel's WEEKNUM uses Sunday-start weeks unless you give it a return type. In Outlook, set the first week of the year to First 4-day week and the first day of the week to Monday. In Excel, use ISOWEEKNUM(date) or WEEKNUM(date,21). See the Excel guide and the calendar guide.
When does week 1 of 2027 start?
Week 1 of 2027 runs Monday, January 4 – Sunday, January 10, 2027.