Week Number
About the Week Number
Payroll cycles, manufacturing reports, academic timetables, and sprint planning often reference week numbers instead of month names-especially in Europe where ISO week dating is standard. This week number calculator takes any calendar date and returns its ISO 8601 week number along with the Monday-start week boundaries that define that week. ISO rules can surprise you: 1 January sometimes belongs to week 52 or 53 of the previous year, and late December dates may already be week 1 of the next year. Rather than memorizing those edge cases, pick a date and read the authoritative week index plus the exact start and end dates of that week.
How to use it
- Select the date you want to evaluate-past, present, or future.
- Click Get week number to run the ISO week lookup.
- Read the week number and ISO week-year in the result.
- Review week start (Monday) and week end (Sunday) in the detail section.
- Use Copy result when documenting reports or tickets.
Good to know
Results are calendar math from the dates you enter. Business-day tools skip weekends when they say so. They do not know local holidays unless the page says they do.
Frequently asked questions
Is the Week Number free?
Yes. You can use it in your browser with no account and no download.
What standard does the week number calculator use?
ISO 8601: weeks start Monday, week 1 contains the first Thursday of the ISO week-year.
Why can January dates show the previous ISO year?
Days before the first ISO week of the year belong to week 52 or 53 of the prior ISO week-year.
Does week 53 exist every year?
No. Week 53 appears only in ISO years where Thursday-based counting yields 53 weeks.
What are the week start and end dates?
ISO weeks run Monday 00:00 through Sunday end-of-day in local calendar terms.
Related
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