Week Number Calculator
Free online week number calculator. Find the ISO week number for any date, plus US and Islamic week numbering systems.
About This Free Online Week Number Calculator
Our free online week number calculator finds the week number (1-53) for any date using three different systems: ISO 8601 (international standard), US/北美 (week containing January 1), and Islamic (Saturday-based week). Displays the week date range, the current week's start and end dates, and the total weeks in the selected year.
Features of Our Week Number Calculator
- ISO 8601 week number for any date
- US/North American week numbering system
- Islamic week numbering system
- Week date range (start and end dates)
- Total weeks in selected year
- Real-time results as you pick a date
How to Use the Week Number Calculator
Using this tool is simple and requires no signup or registration. Follow these steps:
- Select a date using the date picker or click Today.
- View the week number in all three numbering systems.
- See the week date range and total weeks in the year.
- Switch between systems to compare week numbering.
Frequently Asked Questions About Week Number Calculator
What is ISO week date?
ISO 8601 week numbering defines week 1 as the week containing the first Thursday of the year. Weeks start on Monday. This is the international standard used in most European and Asian countries.
What is the US week numbering system?
In the US system, week 1 is the week containing January 1. Weeks start on Sunday. This system is used in the United States, Canada, and most of Latin America.
How many weeks are in a year?
A year has either 52 or 53 weeks. There are 52 weeks plus 1 day (or 2 in a leap year), which means some years have a 53rd week depending on the numbering system.
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