NETWORKDAYS(...)
Using NETWORKDAYS formula
Used Functions
Category: Date and time
Returns the number of whole workdays between two dates
Syntax
NETWORKDAYS(start_date, end_date, [holidays])
Practice NETWORKDAYS Formula at Sheetzoom
NETWORKDAYS formula at Microsoft help
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The formula needs three arguments, first and the second are starting and the end date, the third one is an optional argument and it takes date range of holidays from the worksheet, thus returning the result.