A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Use absolute referencing. For example, if the holidays are specified on Sheet2 in A2:A50, use a formula such as
=WORKDAY(D1, 180, Sheet2!$A$2:$A$50)
where D1 contains a starting date and 180 is the duration in days. This formula can be filled down. The $ iin $A$2:$A$50 ensure that this reference won't change.
Even easier: select the range with holiday dates (A2:A50 on Sheet2 in our example). Then click in the address box on the left hand side of the formula bar, type the name Holidays and press Enter. You can now refer to the range by its name:
=WORKDAY(D1, 180, Holidays)