Week Calculator
Find ISO week number for any date
Table of Contents
How to Use
- Select or enter a date
- Click calculate to see the week number
- View ISO week number and year
- See which day of the week it is
What is ISO Week Date System?
The ISO week date system is an international standard (ISO 8601) for numbering weeks. Week 1 of a year is the week containing the first Thursday of the year, which is equivalent to the week containing January 4th.
This system ensures that each week belongs to exactly one year, making it ideal for business, manufacturing, and financial planning.
How Weeks Are Numbered
- Week 1 is the first week with a Thursday
- Weeks run from Monday to Sunday
- A year has 52 or 53 weeks
- Week numbering is consistent across countries using ISO standard
Common Uses of Week Numbers
- Project planning and scheduling
- Manufacturing and production planning
- Business reporting and analytics
- Delivery scheduling
- Academic calendars
- Retail planning
- Construction timelines
Frequently Asked Questions
- Why doesn't Week 1 always start on January 1st?
- ISO week 1 is defined as the week containing the first Thursday of the year. This ensures each week belongs entirely to one year and provides consistency in business planning.
- Can a year have 53 weeks?
- Yes, years that start on Thursday or leap years starting on Wednesday have 53 weeks.
- Do all countries use ISO week numbering?
- No, while many European and business contexts use ISO weeks, some countries like the US use different systems. Always clarify which system is being used.
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