Suppose you need to find a date, such as an invoice due date or project end date that occurs a number of workdays (Monday through Friday) before or after a certain date. It's easy using the WORKDAY function.
Imagine that you have approximately 80 workdays in which to complete a project that begins on 12/31/2010, and you need to find the project end date. First you would enter those values into cells A2 and A3 as shown in the picture. Next, you would enter the dates of any holidays likely to affect the calculation, each holiday in its own cell. Then you would type the formula into an empty cell:
The project must be completed by 4/22/2011. Excel added 80 days (cell A3), automatically excluding weekends as well as the holidays in this period listed in the argument A4:A6 (the colon indicates a range of cells). A comma separates each individual argument. The parentheses separate the arguments from the function.