Excel Formula To Calculate Day Of Week From Date

Complete Guide: Excel Formula to Calculate Day of Week from Date

Calculating the day of the week from a given date is a common requirement in Excel for scheduling, reporting, and data analysis. This comprehensive guide covers all methods to determine the weekday from any date in Excel, including formulas, functions, and practical applications.

Why Calculate Day of Week in Excel?

• Scheduling: Automatically determine workdays vs. weekends
• Data Analysis: Group data by weekday for trends
• Reporting: Create dynamic reports that change based on the current day
• Financial Modeling: Calculate business days for projections

Method 1: Using the WEEKDAY Function (Most Common)

The WEEKDAY function is Excel’s built-in solution for this calculation. Its syntax is:

=WEEKDAY(serial_number, [return_type])

Parameters:

• serial_number: The date you want to evaluate (can be a cell reference or date value)
• [return_type] (optional): Determines the numbering system (1-3)

Return Type	Description	Example (for 10/15/2023)
1 or omitted	Numbers 1 (Sunday) through 7 (Saturday)	1 (Sunday)
2	Numbers 1 (Monday) through 7 (Sunday)	7 (Sunday)
3	Numbers 0 (Monday) through 6 (Sunday)	6 (Sunday)

Example Usage:

=WEEKDAY(“10/15/2023”) // Returns 1 (Sunday in type 1 system)
=WEEKDAY(A2, 2) // Returns weekday number for date in cell A2 (Monday=1)

Method 2: Using TEXT Function for Day Names

When you need the actual day name instead of a number:

=TEXT(date, “dddd”) // Returns full day name (e.g., “Monday”)
=TEXT(date, “ddd”) // Returns abbreviated day name (e.g., “Mon”)

Example:

=TEXT(“10/15/2023”, “dddd”) // Returns “Sunday”
=TEXT(A2, “ddd”) // Returns “Sun” for date in A2

Method 3: Advanced Formula for Custom Week Start

For scenarios where your week starts on a day other than Sunday or Monday:

=MOD(WEEKDAY(date)-start_day,7)+1

Where start_day is:

• 1 for Sunday
• 2 for Monday
• 3 for Tuesday, etc.

Method 4: Using Power Query (For Large Datasets)

1. Load your data into Power Query Editor
2. Select the date column
3. Go to Add Column > Date > Day > Name of Day
4. Choose your format (full name or abbreviated)

Performance Comparison of Methods

Method	Calculation Speed	Flexibility	Best For	Volatility
WEEKDAY function	Very Fast	High	Most use cases	Non-volatile
TEXT function	Fast	Medium	Display purposes	Non-volatile
Custom formula	Fast	Very High	Special week starts	Non-volatile
Power Query	Medium	High	Large datasets	N/A
VBA	Fast	Very High	Automation	Volatile

Practical Applications

1. Highlighting Weekends in Conditional Formatting

1. Select your date range
2. Go to Home > Conditional Formatting > New Rule
3. Use formula: =OR(WEEKDAY(A1)=1,WEEKDAY(A1)=7)
4. Set your formatting (e.g., light red fill)

2. Counting Weekdays Between Dates

=NETWORKDAYS(start_date, end_date, [holidays])

3. Creating Dynamic Weekday Reports

Combine with FILTER or other dynamic array functions in Excel 365:

=FILTER(data_range, WEEKDAY(date_range,2)<=5, "No weekdays")

Common Errors and Solutions

Error	Cause	Solution
#VALUE!	Invalid date format	Ensure cell contains valid date or use DATEVALUE()
#NUM!	Date out of range (before 1/1/1900)	Use newer Excel version or adjust dates
Wrong day number	Incorrect return_type	Verify your return_type parameter (1, 2, or 3)
#NAME?	Misspelled function	Check function spelling (WEEKDAY, not WEEKDAY)

Historical Context: The Zeller’s Congruence Algorithm

Before Excel functions existed, mathematicians used algorithms like Zeller’s Congruence to calculate the day of the week for any Julian or Gregorian calendar date. The algorithm was developed by Christian Zeller in 1883 and remains an important concept in computer science.

The formula for the Gregorian calendar is:

h = (q + floor((13(m+1))/5) + K + floor(K/4) + floor(J/4) + 5J) mod 7

Where:

• h is the day of the week (0 = Saturday, 1 = Sunday, 2 = Monday, …, 6 = Friday)
• q is the day of the month
• m is the month (3 = March, 4 = April, …, 14 = February)
• K is the year of the century (year mod 100)
• J is the zero-based century (floor(year / 100))

Excel vs. Other Tools

Tool	Day of Week Function	Syntax Example	Notes
Excel	WEEKDAY()	=WEEKDAY(A1)	Most flexible with return_type
Google Sheets	WEEKDAY()	=WEEKDAY(A1)	Same syntax as Excel
JavaScript	getDay()	date.getDay()	Returns 0-6 (Sunday-Saturday)
Python	weekday()	date.weekday()	Returns 0-6 (Monday-Sunday)
SQL	DATEPART()	DATEPART(weekday, date)	Syntax varies by DBMS

Authoritative Resources

For additional technical details about date calculations:

• National Institute of Standards and Technology (NIST) – Time and Frequency Division
• Mathematical Association of America – Historical Mathematical Algorithms
• Library of Congress – Science Reference Services: Days of the Week

Best Practices for Date Calculations in Excel

1. Always validate dates: Use ISNUMBER with DATEVALUE to check valid dates
2. Document your return_type: Add comments explaining which numbering system you’re using
3. Consider time zones: For international data, account for time zone differences
4. Use table references: Convert ranges to tables for more reliable references
5. Test edge cases: Verify calculations for leap years and century changes
6. Consider performance: For large datasets, WEEKDAY is more efficient than TEXT
7. Handle errors gracefully: Use IFERROR to manage invalid dates

Advanced: Creating a Custom Weekday Function with VBA

For specialized needs, you can create a custom function:

Function CUSTOM_WEEKDAY(d As Date, Optional startDay As VbDayOfWeek = vbSunday) As String Dim weekdayNum As Integer weekdayNum = Weekday(d, startDay) Select Case weekdayNum Case 1: CUSTOM_WEEKDAY = “Sunday” Case 2: CUSTOM_WEEKDAY = “Monday” Case 3: CUSTOM_WEEKDAY = “Tuesday” Case 4: CUSTOM_WEEKDAY = “Wednesday” Case 5: CUSTOM_WEEKDAY = “Thursday” Case 6: CUSTOM_WEEKDAY = “Friday” Case 7: CUSTOM_WEEKDAY = “Saturday” End Select End Function

Usage in Excel: =CUSTOM_WEEKDAY(A1) or =CUSTOM_WEEKDAY(A1, 2) for Monday start

Future-Proofing Your Date Calculations

Excel’s date system has limitations:

• Only handles dates from 1/1/1900 to 12/31/9999
• 1900 isn’t a leap year in Excel (historical bug)
• Time zone information isn’t stored with dates

For enterprise applications, consider:

• Using dedicated date libraries
• Storing dates in ISO 8601 format (YYYY-MM-DD)
• Implementing proper time zone handling