Week Calculator
Enter any date to instantly see its ISO week number, which quarter it falls in, what day of the year it is, how many days remain in the year, and the full week date range (Monday through Sunday).
- ISO week number of the year
- Quarter (Q1, Q2, Q3, Q4)
- Day of year and days remaining
- Week start (Monday) and end (Sunday)
Week Number Lookup
How to Use the Week Calculator
Select any date using the date picker and click “Calculate.” The tool immediately shows the ISO week number, quarter, day of the year, days remaining in the year, and the full Monday-to-Sunday date range for that week.
About ISO Week Numbers
ISO 8601 defines weeks as starting on Monday and ending on Sunday. Week 1 is the week containing the first Thursday of the year. This standard is widely used in business, manufacturing, and international scheduling. Our calculator follows the ISO standard precisely.
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Frequently Asked Questions
Common questions about week calculations
ISO 8601 is an international standard for date representation. Under this standard, weeks start on Monday, and Week 1 is defined as the week containing the first Thursday of January. This means some years have 52 weeks and others have 53.
Some calendars start weeks on Sunday (common in the US), while ISO weeks always start on Monday. Our calculator uses the ISO standard, which is the most widely used in business and international contexts.
Yes! A year has 53 ISO weeks when January 1 falls on a Thursday, or when December 31 falls on a Thursday. This happens roughly every 5-6 years. The calculator handles this automatically.
Quarters divide the year into four equal parts: Q1 (January-March), Q2 (April-June), Q3 (July-September), and Q4 (October-December). They are commonly used in business for financial reporting and planning.