Stay in sync with international business standards using the ISO Week Number Calculator. Professional project management often relies on week numbers (W01-W53) for scheduling and reporting. Our tool accurately calculates the ISO-8601 week number for any date, helping you coordinate timelines across global teams and maintain consistent production calendars.
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ISO Week Number Calculator
Quickly find the ISO-8601 week number for any date. Accurate calculation following international standards.
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Select Date
Choose a date to calculate its week number
Result
ISO-8601 Standard
Week Number
11
Year 2026
What is the ISO Week Date System?
The ISO week date system is part of the ISO 8601 date and time standard. It is used primarily in government and business for fiscal years, as well as in timekeeping.
- Week 1 is the week with the year's first Thursday in it.
- Monday is the first day of the week.
- A year has either 52 or 53 full weeks.
About ISO Week Number Calculator
1
Select Date
Pick a date using the calendar picker or type it in manually.
2
Calculate
The ISO week number is calculated instantly for the chosen date.
3
View Details
See the week number, year, and range of dates for that week.
4
Copy
Copy the week number for your project reports or schedules.
Key Features
ISO-8601 Compliance
Follows the official international standard for identifying weeks in the year.
Range Calculation
See the exact start and end dates for the identified week number.
Year Context
Correctly handles transition weeks that span across two calendar years.
Frequently Asked Questions
Yes, we follow the international ISO-8601 standard for week numbering.
The first week of the year is the one that contains the first Thursday of January.
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