Week Number Calculator
Instantly find the week number for any date. Supports ISO 8601 and US week numbering. Full year calendar with all week numbers included.
Current Week
Week 24
Day of Year
Day 160
Year Progress
43.8%
Days Left in Year
205
Tue, Jun 9, 2026
Week 24
ISO 8601 week number
Week starts
Mon, Jun 8, 2026
Week ends
Sun, Jun 14, 2026
Days left in this week: 5
- Week Number
- 24
- Day of Year
- 160
- Quarter
- Q2
- Days Left in Year
- 205
- Week Start
- Mon, Jun 8, 2026
- Week End
- Sun, Jun 14, 2026
📅 Full Year Calendar — Week Numbers 2026
How to use Week Number Calculator
The week number calculator displays the ISO 8601 week number for any date, the start and end of that week, the day of the year (day 1–366), the quarter, the days remaining in the year and whether the date falls in a leap year. ISO week 1 is defined as the week containing the first Thursday of the year.
- Select a date or use today's date.
- View the week number, week boundaries, day of year, quarter and year summary.
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ISO 8601 week numbering explained
The ISO 8601 standard defines weeks starting on Monday. Week 1 is the week containing January 4th (equivalently, the week with the year's first Thursday). This means December 29–31 may belong to week 1 of the following year, and January 1–3 may belong to week 52 or 53 of the previous year. The ISO year can differ from the Gregorian calendar year at year boundaries.
Glossary
- ISO 8601
- International standard for date and time representations, including week numbering.
- Leap year
- A year with 366 days (February has 29 days) occurring every 4 years, with century exceptions.
Related reading
Frequently Asked Questions
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Why use Week Number Calculator?
- Handles timezone conversions and DST automatically
- Supports date arithmetic across years and leap years
- ISO 8601 and human-readable output formats
- Works for historical and future dates with full accuracy
Common use cases
- Calculate how many days until a project deadline
- Find the day of the week for a date in the past
- Convert meeting times across different time zones
- Calculate age from a date of birth
- Add or subtract business days for contract terms
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