ISO 8601 Week Number Calculator
Find the current ISO 8601 week number, determine start and end dates for any calendar week, and look up which week any date belongs to. Essential for corporate planning, production schedules, and agile sprints directly inside your web browser with complete privacy.
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Step-by-Step Guide: How to Use Week Number Calculator Online
- 1Pick any calendar date (or keep today's date).
- 2View the ISO week number (e.g. Week 36) and its Monday-to-Sunday span.
- 3Review year progress percentage and total weeks in the year.
- 4Use the reverse lookup tool below if you need dates for a future week.
Week Number Calculator Features & Capabilities
- Compliant with international standard ISO 8601 calendar weeks
- Shows exact week start (Monday) and end (Sunday) dates
- Calculates percentage of year passed and remaining weeks in the year
- Reverse lookup: Convert any Year + Week number into its exact date range
- One-click 'Current Week' button for instant today lookup
Technical Specifications & Privacy Standards
| Supported Formats | Calendar Dates |
| Execution Architecture | 100% Client-Side WebAssembly & HTML5 Canvas (Local CPU/GPU) |
| Server File Transfer | 0 Bytes Transferred (Zero Cloud Uploads) |
| Output Quality | Lossless Vector & Original Resolution Maintained |
| Compatibility | Cross-Platform (Windows, macOS, Linux, iOS, Android) |
Your files are processed locally in your browser memory and are not uploaded to our file-processing servers.
Week Number Calculator FAQ
What is the ISO 8601 standard for week numbers?
Under ISO 8601, weeks begin on Monday, and Week 1 of the year is the week containing the first Thursday of that calendar year (or January 4).
Can a year have 53 ISO weeks instead of 52?
Yes. Years that begin on a Thursday (or leap years starting on Wednesday) contain 53 full ISO calendar weeks.
Can I look up the exact date range for a specific week number?
Yes. Select any week number and year to view the exact Monday start date and Sunday end date for that designated period.
Does this tool support both US and international week systems?
The calculator defaults to the international ISO 8601 standard (Monday-Sunday) while providing reference for Sunday-start systems.
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