The formula for the WORKDAY function is WORKDAY(start_date, days, [holidays]). The syntax for the WORKDAY function is below:
Start_date: A date that represents the start date. It is required.
Days: The number of non-weekend days and non-holiday days before or after the start date. It is required.
Holidays:  Dates to exclude from the working calendar, such as state, federal holidays, and floating holidays.