RE spreadsheet formulas ...

in A1 put =TODAY().
in A2 put a future date.

Somewhere else put =A1-A2 and hit Enter. Be sure to format as "Number." This gives the number of days into the future the other date is.
Using the today() function is advantageous because if you open your spreadsheet in the future it will reassess "today" and adjust it's output accordingly.

Now in column B make a list of holidays (for example in B1:B20).

Somewhere else put =NETWORKDAYS(A1,A2,B1:B20) and hit Enter. This does the same, except it excludes weekends and whatever dates are in the holiday list.

-steve

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steve