Excel WEEKDAY Function: Complete Guide to Day of Week Commands

The Excel WEEKDAY function is a powerful date and time function that returns a numeric value representing the day of the week for a given date. This essential function enables users to perform day-based calculations, create conditional formatting rules, and build sophisticated date analysis formulas in their spreadsheets.

Understanding the WEEKDAY Function Syntax

The WEEKDAY function follows a straightforward syntax structure that accepts two parameters:

=WEEKDAY(serial_number, [return_type])

Function Parameters Explained

serial_number (Required): This parameter represents the date for which you want to find the day of the week. You can input this as:

• A direct date value (e.g., “2024-01-15”)
• A cell reference containing a date
• A serial number representing a date
• The result of another date function

return_type (Optional): This parameter determines how the function numbers the days of the week. When omitted, Excel defaults to system 1.

Return Type Systems in Detail

Excel’s WEEKDAY function offers seven different return type systems, each numbering the days of the week differently:

System 1 (Default): Sunday = 1

• Sunday: 1
• Monday: 2
• Tuesday: 3
• Wednesday: 4
• Thursday: 5
• Friday: 6
• Saturday: 7

System 2: Monday = 1

• Monday: 1
• Tuesday: 2
• Wednesday: 3
• Thursday: 4
• Friday: 5
• Saturday: 6
• Sunday: 7

System 3: Monday = 0

• Monday: 0
• Tuesday: 1
• Wednesday: 2
• Thursday: 3
• Friday: 4
• Saturday: 5
• Sunday: 6

Systems 11-17: Specialized Numbering

Excel also provides systems 11 through 17, which offer alternative starting points for specific regional or business requirements. These systems maintain consecutive numbering but begin with different days of the week.

Practical WEEKDAY Function Examples

Basic Usage Examples

Here are fundamental examples demonstrating the WEEKDAY function in action:

=WEEKDAY("2024-06-09")
Returns: 1 (Sunday using default system)

=WEEKDAY("2024-06-09", 2)
Returns: 7 (Sunday using Monday=1 system)

=WEEKDAY(TODAY())
Returns: Current day number based on today's date

Advanced Formula Combinations

Combining WEEKDAY with other functions creates powerful date analysis tools:

=IF(WEEKDAY(A1)=1, "Weekend", "Weekday")
Identifies weekend vs weekday dates

=CHOOSE(WEEKDAY(A1), "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat")
Converts numeric day to text abbreviation

Business Applications and Use Cases

Payroll Calculations

Use WEEKDAY to calculate weekend premiums or different hourly rates based on the day of the week:

=IF(OR(WEEKDAY(A1)=1, WEEKDAY(A1)=7), B1*1.5, B1)
Applies weekend premium rate

Project Planning

Exclude weekends from project timelines by identifying business days:

=IF(AND(WEEKDAY(A1)>1, WEEKDAY(A1)<7), "Business Day", "Weekend")
Identifies business days for scheduling

Sales Analysis

Analyze sales patterns by day of the week to optimize staffing and inventory:

=SUMIF(WEEKDAY(DateRange), 2, SalesRange)
Sums Monday sales across date range

Common Errors and Troubleshooting

#VALUE! Error

This error occurs when Excel cannot recognize the date format in your serial_number parameter. Ensure your date is in a recognizable format or use proper date functions like DATE() to construct valid dates.

#NUM! Error

This error appears when the return_type parameter is not within the valid range (1-3, 11-17). Double-check your return_type value to ensure it matches one of Excel’s supported systems.

Incorrect Day Returns

If the function returns unexpected day numbers, verify that you’re using the correct return_type system for your needs. Different systems start the week on different days.

Performance Optimization Tips

Array Formula Efficiency

When applying WEEKDAY to large data ranges, consider using array formulas or Excel’s newer dynamic array functions for better performance:

=WEEKDAY(A1:A1000, 2)
Processes entire range efficiently

Conditional Formatting Integration

Use WEEKDAY in conditional formatting rules to highlight weekends or specific days:

=OR(WEEKDAY($A1)=1, WEEKDAY($A1)=7)
Highlights weekend dates in your range

Advanced Techniques and Best Practices

Dynamic Week Start Configuration

Create flexible formulas that allow users to configure which day starts the week:

=WEEKDAY(A1, IF(B1="Monday", 2, IF(B1="Sunday", 1, 3)))
Adjusts week start based on user preference

Multi-Language Support

Combine WEEKDAY with lookup tables for international day name support:

=INDEX(DayNames, WEEKDAY(A1))
Returns day name in preferred language

Integration with Other Excel Functions

DATE Function Combinations

Use WEEKDAY with DATE functions for complex date calculations:

=WEEKDAY(DATE(YEAR(A1), MONTH(A1), 1))
Returns first day of month's weekday

NETWORKDAYS Integration

Combine with NETWORKDAYS for sophisticated business day calculations:

=NETWORKDAYS(A1, B1) - SUMPRODUCT((WEEKDAY(ROW(INDIRECT(A1&":"&B1)), 2)>5)*1)
Excludes specific weekdays from calculations

Version Compatibility and Limitations

The WEEKDAY function is available in all modern versions of Excel, including Excel 2016, 2019, 2021, and Microsoft 365. The function maintains backward compatibility across versions, ensuring your formulas work consistently across different Excel installations.

Mobile and Web App Support

Excel’s mobile and web applications fully support the WEEKDAY function, making your date analysis formulas portable across platforms. However, some advanced array formula combinations may require the desktop version for optimal performance.

Alternative Approaches and Related Functions

TEXT Function Alternative

For simple day name extraction, consider using the TEXT function:

=TEXT(A1, "dddd")
Returns full day name (e.g., "Monday")

FORMAT Function in Newer Versions

Excel 365 users can leverage the FORMAT function for more flexible date formatting:

=FORMAT(A1, "ddd")
Returns abbreviated day name

The Excel WEEKDAY function serves as a cornerstone for date-based analysis and automation in spreadsheets. By mastering its syntax, understanding the various return type systems, and implementing the advanced techniques outlined in this guide, you can build sophisticated date analysis solutions that enhance your Excel productivity and analytical capabilities.