Microsoft Excel has several builtin WORKDAY functions that can be used for date calculations. Each function does a different job and the results differ from one function to the next.
Instructions in this article apply to Excel 2019, 2016, 2013; and Excel for Office 365.
WORKDAY Function Syntax and Arguments
The WORKDAY function finds the start or end date of a project or assignment when given a set number of work days. The number of work days automatically excludes weekends and any dates that are identified as holidays.
The WORKDAY function you use will depend on the results you want, which may include one of the following:
 Finding the end date for a project with a set number of work days following a given start date.
 Finding the start date for a project with a set number of work days before a given end date.
 Finding the due date for an invoice.
 Finding the expected delivery date for goods or materials.
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 will be 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.
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.
Enter the WORKDAY Function
This tutorial 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 are not counted as part of the 82 days.
To avoid calculation problems that occur if dates are accidentally entered as text, the DATE function is used to enter the dates in the function. See the Error Values section at the end of this tutorial for more information.
Begin by entering the following data into the indicated cells:
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.
To create the WORKDAY function:

Select cell E5 to make it the active cell. This is where the results of the WORKDAY function will be displayed.

Select Formulas.

Choose Date & Time > WORKDAY to display the Function Arguments dialog box.

Place the cursor in the Start_date text box. You'll see the beginning of the formula in cell E5.

Select cell E1 in the worksheet to enter this cell reference into the dialog box.

Place the cursor in the Days text box.

Select cell E2 in the worksheet to enter this cell reference into the dialog box.

Place the cursor in the Holidays text box.

Drag to select cells E3 and E4 in the worksheet to enter these cell references into the dialog box.

Select OK in the dialog box to complete the function. Except on a Mac, where you select Done instead.

The date 11/2/2012, the end date for the project, appears in cell E5 of the worksheet.

When you select cell E5, the complete function appears in the formula bar above the worksheet.
=WORKDAY(E1,E2,E3:E4)
Troubleshoot WORKDAY Function Errors
If the data for the various arguments of this function are not entered correctly, an error values appear in the cell where the WORKDAY function is located.
You will see one of these errors:
 #VALUE! appears in the answer cell if one of the WORKDAY 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 is truncated, rather than rounded up or down, to the integer portion of the number (for example, 82 days).