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The week number comes from your device’s own date and refreshes on its own, so it is never out of date.
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What Week Is It?
See what week it is right now, with the current week number, its start and end dates, and how much of the year is left. Switch between ISO 8601 and US week numbering, look up the week of any date, or browse every week of the year.
Current week number
Today
Week–
- Day of year
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- Days left
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- Weeks left
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- Quarter
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- ISO week date
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- Day of week
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Year progress–
Find the week number of any date
Week number
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Find the dates of a week
Week dates
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Week numbers
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Features
More than just “what week is it”
Most week number sites show a single number and a wall of ads. This tool answers the question instantly, then gives you everything you need to plan around it.
ISO and US systems
Switch between ISO 8601 weeks, which start on Monday, and US weeks, which start on Sunday.
Any date, any week
Look up the week number of a date, or the exact start and end dates of any week in any year.
Full year at a glance
Browse all 52 or 53 weeks of any year, with the current week highlighted and past weeks faded.
Year progress
See the day of the year, days and weeks left, the quarter and a live progress bar for the year.
Copy and share
Copy a clean line such as “Week 12, Mon 16 Mar to Sun 22 Mar” for emails, timesheets or sprint notes.
How it works
How to use this week number tool
The answer to “what week is it” appears as soon as the page loads. Use these steps for everything else.
Check today’s week
Read the large week number at the top, plus its Monday to Sunday date range.
Pick your system
Choose ISO 8601 for Europe and most of Asia, or US for Sunday-start calendars.
Convert dates and weeks
Enter a date to get its week, or a year and week to get its dates.
Browse the year
Use the arrows to move between years and see every week at once.
The rules
How week numbers are calculated
There is more than one way to number the weeks of a year. So the answer to “what week is it” can differ by one, depending on the system your calendar uses.
| Rule | ISO 8601 | US |
|---|---|---|
| First day | Monday | Sunday |
| Week 1 | Week with the year’s first Thursday | Week that contains 1 January |
| Weeks per year | 52 or 53 | 53, or 54 in rare years |
| Partial weeks | Never, weeks are always 7 days | First and last weeks can be short |
| Used in | Europe, most of Asia, business and IT | USA, Canada, Japan |
- The 4 January rule. ISO week 1 always contains 4 January, so it can start as early as 29 December of the year before.
- Week 53 years. An ISO year has 53 weeks when it starts on a Thursday, or on a Wednesday in a leap year. Examples include 2015, 2020, 2026 and 2032.
- ISO week dates. ISO writes a date as year, week and day, such as
2026-W12-3for the Wednesday of week 12. - In spreadsheets. Use
=ISOWEEKNUM(A1)for ISO weeks, or=WEEKNUM(A1)for Sunday-start weeks in Excel and Google Sheets.
Benefits
Who uses week numbers?
Week numbers make planning shorter and clearer. Instead of two dates, you share one number.
Project teams
Plan sprints, releases and deadlines by week, and keep every team on the same schedule.
Payroll and HR
Track pay periods, timesheets and leave by week number without confusion over dates.
Retail and logistics
Compare sales, shipments and stock levels week over week, and year over year.
Schools and students
Follow term plans, timetables and revision schedules that are set out by week.
FAQ
Week number FAQs
Quick answers to the most common questions about week numbers.
What week is it right now?
The current week number is shown in large type at the top of this page. It comes from your device’s date and uses the ISO 8601 standard by default. Switch to US to see Sunday-start numbering.
How many weeks are in a year?
A year has 52 weeks plus one extra day, or two extra days in a leap year. As a result, an ISO year has either 52 or 53 numbered weeks.
When does week 1 start?
In the ISO system, week 1 is the week that contains the first Thursday of January, which is also the week with 4 January. In the US system, week 1 is simply the week that contains 1 January.
Does the week start on Monday or Sunday?
It depends on the system. ISO 8601, used across Europe and in most business software, starts weeks on Monday. The US, Canada and Japan usually start weeks on Sunday.
What is week 53?
Week 53 is an extra week that appears in some years. In ISO numbering, it happens when a year starts on a Thursday, or on a Wednesday in a leap year. 2026 is one of those years.
How do I find the week number in Excel?
Use =ISOWEEKNUM(A1) for the ISO week of the date in cell A1. For Sunday-start weeks, use =WEEKNUM(A1). You can also use =WEEKNUM(A1,21) to get ISO weeks.
Why does my calendar show a different week number?
Your calendar probably uses the other system. Near the start and end of the year, ISO and US numbers can differ by one week. Match the setting here to your calendar and the numbers will line up.
Know the week, plan the week
Bookmark this page and you will always know what week it is. Use the date and week converters for planning ahead, then try our other date tools below.
See the current weekWeek numbers are based on the date set on your device. ISO 8601 rules follow the international standard for dates and times.