Introduction to Excel Week Numbers
The week number in Excel is a useful way to track and organize dates by their corresponding weeks in a year 📅. Whether you are managing project deadlines, reporting weekly sales, or scheduling tasks, Excel makes it easy to calculate the week number from any date.
This feature works seamlessly across Windows, macOS, and Ubuntu via LibreOffice, making it a reliable solution for time-based data management in any environment.
What Is the WEEKNUM Function
The WEEKNUM() function is a built-in Excel feature that returns the week number of a date. This number ranges from 1 to 52 (or sometimes 53 depending on the year).
For example:
=WEEKNUM("2024-01-01")
Returns: 1
It’s a straightforward tool that simplifies calendar-related calculations for business reports, timelines, and dashboards.
Syntax of WEEKNUM Explained
The basic syntax is:
=WEEKNUM(serial_number, [return_type])
- serial_number: The date you want to convert
- return_type (optional): Determines which day the week starts on
Default behavior assumes weeks start on Sunday, but you can change it using the return type.
WEEKNUM Return Type Options
| Return Type | Week Starts On | Description |
|---|---|---|
| 1 | Sunday | Default for U.S. system |
| 2 | Monday | Common in Europe |
| 11–17 | Monday–Sunday | For custom week starts |
| 21 | ISO 8601 | European ISO week system |
For example, to start your week on Monday:
=WEEKNUM(A1, 2)
To follow ISO standard:
=ISOWEEKNUM(A1)
WEEKNUM vs ISOWEEKNUM
| Function | Week Start | Rule for Week 1 |
|---|---|---|
| WEEKNUM | User-defined | Week of January 1 |
| ISOWEEKNUM | Monday | First week with a Thursday |
✅ Use WEEKNUM for general tracking
✅ Use ISOWEEKNUM for formal reporting and standards
Example 1: Getting Week Number from a Date
If A1 contains:
2024-03-15
Then:
=WEEKNUM(A1, 2)
Returns:
11
This means March 15th falls in the 11th week of the year (starting Monday).
Example 2: Weekly Tracking Sheet
You have a list of dates in column A:
| A (Date) | B (Week No) |
|---|---|
| 01/01/2024 | =WEEKNUM(A2, 2) |
| 08/01/2024 | =WEEKNUM(A3, 2) |
| 15/01/2024 | =WEEKNUM(A4, 2) |
Drag down to generate week numbers dynamically for schedules or reports.
Using WEEKNUM with TODAY Function
To get the current week number:
=WEEKNUM(TODAY(), 2)
This updates automatically each day, making it great for dashboards and real-time reporting.
Referencing Cells with WEEKNUM
Make your formula flexible by using cell references:
=WEEKNUM(B1, C1)
Where:
- B1 contains the date
- C1 contains the return_type (e.g., 1 or 2)
🎯 Helps when building templates or data validation sheets.
Adjusting Start of the Week in WEEKNUM
To start the week on Tuesday:
=WEEKNUM(A1, 3)
Use return types from 11 to 17 for custom starting days, helpful in international projects or company-specific calendars.
WEEKNUM on Windows Excel
- Works in Excel 2010 and newer
- Shortcut: Type
=WEEKNUM(and use Tab to autocomplete - Format cells using Number or Custom formatting
🖥️ Efficient and widely supported across corporate environments
WEEKNUM on macOS Excel
- Fully functional in Excel for Mac
- Shortcut:
Command + Uto enter or edit formulas - Identical syntax and logic to Windows version
🍏 Ideal for Apple-based users managing academic or business data
WEEKNUM in LibreOffice on Ubuntu
LibreOffice Calc supports:
=WEEKNUM(A1; 2)
Note: use a semicolon instead of a comma in some locales
- ISO week support via:
=ISOWEEKNUM(A1)
🐧 A great choice for Linux-based offices and universities
Formatting the Output of WEEKNUM
To keep things readable:
- Format as Number
- Use
TEXT()to add labels:
="Week " & WEEKNUM(A1, 2)
Use in headers, charts, or dashboards for better clarity 📋
Use Cases for Week Numbers in Excel
- 📅 Timesheet and payroll processing
- 📦 Weekly inventory tracking
- 📈 Sales and marketing reporting
- 🧾 Invoice scheduling
- 📚 Academic weekly planning
Knowing the week number keeps timelines and reports consistent across teams.
Common Errors and Fixes with WEEKNUM
| Error | Cause | Fix |
|---|---|---|
#VALUE! | Invalid date format | Ensure date cells are formatted correctly |
| Wrong week | Wrong return_type used | Double-check if you want ISO or US style |
| Extra commas | Incorrect syntax on Linux | Use semicolons if required by locale |
Always validate input data before applying time functions.
Automating Week Labels with TEXT and CONCAT
Create dynamic labels:
="Week " & WEEKNUM(A2, 2) & ": " & TEXT(A2, "mmm dd")
Result:
Week 14: Apr 02
Great for dashboards, Gantt charts, or visual calendars.
Using WEEKNUM with IF for Scheduling Logic
Example: Flag overdue weeks
=IF(WEEKNUM(A1, 2)<WEEKNUM(TODAY(), 2), "Past Due", "Upcoming")
📌 Enables smart alerts and filters for time-based tasks.
FAQs About Excel Week Number
What is the default start day for WEEKNUM?
Sunday, unless you specify a different return_type.
What’s the difference between WEEKNUM and ISOWEEKNUM?
WEEKNUM starts from Jan 1. ISOWEEKNUM follows the ISO 8601 standard, where week 1 is the first week with a Thursday.
Can I change the week start day?
Yes. Use return types from 1 to 17 for different start days.
Is WEEKNUM available on macOS and Ubuntu?
Yes. It works on Excel for Mac and LibreOffice Calc on Linux.
Does WEEKNUM work with date ranges?
Yes. Just apply the formula to a range of dates using the fill handle.
Final Thoughts on Excel Week Number
The Excel week number feature is a simple but powerful way to bring order and clarity to date-based data. Whether you’re using WEEKNUM() or ISOWEEKNUM(), Excel gives you flexibility across Windows, macOS, and Ubuntu to calculate weeks for schedules, analytics, and reports.
By understanding the syntax, return types, and formatting options, you’ll unlock a new level of date management inside your spreadsheets.
Complete List of Windows Keyboard Shortcuts
If you need help for Windows, you can find a whole list of all keyboard shortcuts here.
https://keyboard-shortcuts.org/
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