Current Week Number
About ISO-8601 Week Numbers
Week numbers follow the ISO-8601 standard, where weeks start on Monday. The first week of the year is the week that contains that year's first Thursday (also known as the "First 4-day week"). This standard is widely used in business, project management, and international date formatting. Understanding week numbers is essential for scheduling, reporting, and date calculations in various applications.
Related tools: Check out our Weeks by Year calculator to view all weeks for a specific year, or use our Day Numbers tool to calculate the day of the year. For more date and time utilities, visit our Tools page.
Note: ISO 8601 is not the only week numbering system in the world. Other systems use weeks starting on Sunday (US) or Saturday (Islamic).
Programming Routines
Learn how to get the current week number in various programming languages and databases:
=ISOWEEKNUM(TODAY())
or (in older versions):
=WEEKNUM(TODAY(),21)Where the return type '21' is ISO-8601 (week starting on Monday). In Excel 2007 your best choice is WEEKNUM(TODAY(),2) (2=week starting Monday).
Related Tools
Frequently Asked Questions
What is the current week number?
The current week number is calculated according to the ISO-8601 standard, which defines weeks as starting on Monday and ending on Sunday. Week 1 is the first week of the year that contains at least 4 days.
How do I get the week number in my programming language?
This page provides code examples for getting week numbers in various programming languages including JavaScript, Python, Java, PHP, and more. Each example shows how to calculate ISO-8601 week numbers using standard libraries.
What is the difference between ISO-8601 and other week numbering systems?
ISO-8601 defines weeks as starting on Monday and ending on Sunday, with week 1 being the first week containing at least 4 days. Other systems may use different start days (like Sunday) or different rules for determining week 1.