About Week Number Calculator
Free online ISO week number calculator. Determine the exact ISO 8601 calendar week number (Week 1–53), day of the year (Day 1–366), and business quarter for any date.
Key Capabilities & Features
- ISO 8601 international standard week numbering
- Day of year (1 to 366)
- Days remaining in year
- Calendar quarter (Q1 to Q4)
- One-click today button
How to Use Week Number Calculator
1
Select Date
Choose any calendar date or click Today.
2
View Week Number
Read the official ISO week number and year.
3
Inspect Year Metrics
Check remaining days in the year and current quarter.
Privacy & In-Browser Execution Guarantee
100% in-browser date math. Zero tracking.
Frequently Asked Questions
What is ISO 8601 week 1?
Week 1 is the week with the year's first Thursday, or the week that includes January 4.
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