What is a Week Number Calculator?
A Week Number Calculator helps you find the week number for any date and calculate the date range for a specific week. Whether you're managing projects, planning business quarters, or coordinating with teams, working with week numbers is essential for consistent scheduling and communication.
Key Features:
- Date to Week: Enter any date to find its week number
- Week to Dates: Enter a week number to find start and end dates
- Year Statistics: See weeks per year, day of year, and year progress
- Quick Presets: Fast access to today, start of year, and end of year
- Shareable Results: Copy and share calculations via URL
- Privacy First: All calculations happen in your browser
Why Week Numbers Matter
Week numbers provide a simple, standardized way to reference calendar weeks. Instead of saying "the week of January 15-21," you can simply say "Week 3." This is useful for:
- Project management and timeline tracking
- Business planning and quarterly reporting
- Supply chain and manufacturing operations
- Financial analysis and forecasting
- Team coordination across different regions
Understanding Year Boundaries
An important aspect of week numbering is how calendar years and week years interact at boundaries. Dates near year-end can sometimes belong to a different year's weeks, which is why it's important to use this calculator to verify exact dates.
Late December Edge Cases
The last few days of December (typically Dec 28-31) may belong to Week 1 of the following year rather than the current year's final week.
Early January Edge Cases
The first few days of January (typically Jan 1-3) may belong to the previous year's final week rather than the new year's first week.
Use this calculator when working with dates near year boundaries to ensure accuracy in your planning and reporting.
How to Use This Calculator
Date Mode
Select a date using the date picker or quick presets (Today, Yesterday, Jan 1, Dec 31). The calculator instantly shows you the week number, date range, and year statistics.
Week Mode
Enter a week number and year to find the exact date range for that week. Perfect for scheduling and planning when you know the week but need the specific dates.
Copy & Share
Use the Copy button to save results to your clipboard. The calculator preserves your selection in the URL, so you can easily share calculations with others.
Frequently Asked Questions
How many weeks are in a year?
Most years have 52 weeks. Approximately 1 in every 5-6 years will have 53 weeks. This calculator shows the exact count for any year you query.
Why does my date show a different year's week?
Dates near year boundaries (late December or early January) can belong to a different year's weeks. This is normal and calculated correctly by the tool. Always check the result to see which year the week belongs to.
Can I share my calculation with someone?
Yes! The calculator stores your selection in the URL, so you can copy the URL and share it with others. They'll see the exact same calculation when they open the link.
Is my data private?
Yes. All calculations happen entirely in your browser. Your dates are never sent to any server and are not stored anywhere. Your privacy is completely protected.
Can I convert a week number back to a specific date?
Yes. Switch to Week Mode, enter the week number and year, and the calculator shows you the exact start and end dates for that week.
What if I need to work with historical dates?
This calculator works with any date you enter, including historical dates. The week numbering rules are applied consistently across all dates.