Find Project Start and End Dates Using Excel WORKDAY Function

Excel has several built in date functions that can be used for work day calculations. Each date function does a different job so that the results differ from one function to the next. Which one you use, therefore, depends on the results you want.

Uses for the WORKDAY function include calculating:

  • The end date for a project with a set number of work days following a given start date.
  • The start date for a project with a set number of work days before a given end date.
  • The due date for an invoice.
  • The expected delivery date for goods or materials.
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WORKDAY function syntax and arguments

Excel WorkDay Function

Ted French

The WORKDAY function finds the start or end date of a project or assignment given a set number of work days. The number of work days automatically excludes weekends and any dates that are identified as holidays. A function's syntax refers to the layout of the function and includes the function's name, brackets, and arguments.

The syntax for the WORKDAY function is:

= WORKDAY ( Start_date , Days , Holidays )

Start_date (required) is the start date of the chosen time period. The actual start date can be entered for this argument or the cell reference to the location of this data in the worksheet can be entered instead.

Days (required) specifies the length of the project. This is an integer showing the number of days of work that were performed on the project. For this argument, enter the number of days of work or the cell reference to the location of this data in the worksheet.

To find a date that occurs after the Start_date argument, use a positive integer for Days. To find a date that occurs before the Start_date argument use a negative integer for Days. In this second situation the Start_date argument could be identified as the end date of a project.

Holidays (optional) specifies one or more additional dates that are not counted as part of the total number of working days. Use the cell references to the location of the data in the worksheet for this argument.

Example of finding the end date of a project

This example uses the WORKDAY function to find the end date for a project that begins July 9, 2012 and finishes 82 days later. Two holidays (September 3 and October 8) that occur during this period will not be counted as part of the 82 days.

To avoid calculation problems that can occur if dates are accidentally entered as text, the DATE function will be used to enter the dates used in the function. See the Error Values section at the end of this tutorial for more information.


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Entering the WORKDAY function

Enter the following data into the indicated cell:

D1: Start Date:
D2: Number of Days:
D3: Holiday 1:
D4: Holiday 2:
D5: End Date:
E1: =DATE(2012,7,9)
E2: 82
E3: =DATE(2012,9,3)
E4: =DATE(2012,10,8)

If the dates in cells E1, E3, and E4 do not appear as shown in the image above, check to see that these cells are formatted to display data using the short date format.

  1. Click on cell E5 to make it the active cell; this is where the results of the WORKDAY function will be displayed.
  2. Click on the Formulas tab.
  3. Choose Date and Time functions > WORKDAY from the ribbon to bring up the function's dialog box.
  4. Click on the Start_date line in the dialog box.
  5. Click on cell E1 in the worksheet to enter this cell reference into the dialog box.
  6. Click on the Days line in the dialog box.
  7. Click on cell E2 in the worksheet to enter this cell reference into the dialog box.
  8. Click on the Holidays line in the dialog box.
  9. Drag select cells E3 and E4 in the worksheet to enter these cell references into the dialog box.
  10. Click OK in the dialog box to complete the function
  11. The date 11/2/2012, the end date for the project, should appear in cell E5 of the worksheet.

    How Excel calculates this date is:
    • The date that is 82 days after July 9, 2012 is October 31 (the start date is not counted as one of the 82 days by the WORKDAY function).
    • Add to this date the two holiday dates specified (September 3 and October 8) that were not counted as part of the 82 Days argument. Therefore, the end date of the project is Friday November 2, 2012.
  12. When you click on cell E5 the complete function = WORKDAY ( E1 , E2 , E3 : E4 ) appears in the formula bar above the worksheet
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WORKDAY function error values

If the data for the various arguments of this function are not entered correctly, the following error values appear in the cell where the WORKDAY function is located:

  • #VALUE! appears in the answer cell If one of WORKDAY's arguments is not a valid date (if the date was entered as text for example).
  • #NUM! appears in the answer cell if an invalid date results from adding the Start_date and Days arguments.
  • If the Days argument is not entered as an integer, such as 82.75 days, the number will be truncated, rather than rounded up or down, to the integer portion of the number: 82 days.