ISO Week Number Calculator
Look up the current ISO-8601 week number, calendar week schedule, and date ranges.
Current Week Number
39
Week of Year 2026 (out of 53 weeks)
Week Start (Monday)Monday, Sep 21, 2026
Week End (Sunday)Sunday, Sep 27, 2026
Based on the international standard ISO-8601, where Monday is the first day of the week.
ISO-8601 Week Number Calculator & Calendar Week Finder
Find the current ISO week number, week start date, week end date, and calculate week numbers for any date in the year.
How to Use This Tool
- 1View the current calendar week number according to the international ISO-8601 standard.
- 2Identify the starting Monday date and concluding Sunday date for the active week.
- 3Select any historical or upcoming date in the date picker to lookup its corresponding week number.
Key Features & Capabilities
Standard ISO-8601 Compliance
Guarantees standard international week definitions where Monday is day 1 and Week 1 contains the year’s first Thursday.
52 vs 53-Week Year Detection
Identifies whether the selected calendar year contains 52 or 53 full weeks.
Corporate Work Planning
Indispensable for European corporate manufacturing, logistics sprints, and fiscal planning.
Popular Use Cases
Supply Chain & Manufacturing
Coordinate delivery schedules, shipments, and inventory batches based on work week numbering.
Agile Sprints
Align two-week software engineering sprints with official calendar weeks.
Payroll & Timesheets
Validate employee weekly work hour logs and bi-weekly pay periods.
Frequently Asked Questions (FAQ)
What is the ISO-8601 week standard?
ISO-8601 is the international standard for date and time representation. It establishes that weeks begin on Monday and that the first week of the year is the week containing the first Thursday of the calendar year.