Week Number Calculator
Our Week Number Calculator helps you determine the week number for any date according to different standards. Whether you need ISO 8601 week numbers for international business, US week numbers for domestic planning, or simply want to track your position in the year, this tool provides accurate calculations with detailed week information.
How to Use the Week Number Calculator
- Select a date using the date picker (defaults to today).
- Choose your preferred week numbering standard (ISO 8601 or US).
- Use quick preset buttons to jump to common weeks (current, week 1, etc.).
- View detailed week information, progress, and statistics in real-time.
What Information Do You Get?
- Week Number: The week number according to your selected standard.
- Week Dates: Exact start and end dates for the week.
- Day Information: Day of week name and position within the week.
- Year Progress: How much of the year has passed based on weeks.
- Weeks Remaining: Number of weeks left in the current year.
- Week Overview: Visual grid showing all days in the selected week.
- Statistics: Detailed breakdown of week-related metrics.
Week Numbering Standards
There are two main week numbering systems used worldwide:
ISO 8601 Standard (Monday Start)
- Week starts on Monday and ends on Sunday
- Week 1 is the first week with at least 4 days in the new year
- Week 1 always contains January 4th
- Most commonly used internationally and in business
- Used by most European countries
US Standard (Sunday Start)
- Week starts on Sunday and ends on Saturday
- Week 1 begins on January 1st
- Commonly used in the United States and Canada
- Often used in American business calendars
Understanding Week Numbers
Week numbers are useful for:
- Project Planning: Schedule tasks and milestones by week number
- Business Reporting: Track quarterly and annual performance
- Manufacturing: Production schedules and inventory management
- International Communication: Standardized date references
- Retail: Sales periods and promotional planning
- Education: Academic calendar planning
Week Calculation Formula
The calculator uses precise algorithms based on the selected standard:
- Accounts for leap years and year boundaries
- Handles edge cases where weeks span two years
- Calculates accurate week start and end dates
- Determines quarter and year progress metrics
Common Use Cases
- Planning and scheduling by week numbers
- International business coordination
- Manufacturing and production planning
- Sales and marketing campaign scheduling
- Academic calendar organization
- Project management and milestone tracking
- Time tracking and billing systems
- Shift scheduling and rotation planning
Special Week Considerations
Understanding special cases:
- Week 53: Some years have 53 weeks in ISO 8601 (leap week years)
- Cross-Year Weeks: Week 1 may start in December of the previous year
- Year-End Weeks: Late December dates may belong to Week 1 of next year
- Leap Years: 366 days can affect week calculations
Use our Week Number Calculator for accurate week tracking and planning throughout the year!