To start fill in the day of the weekday number that we want to count in a number field. The weekday number and not its name is important to do a calculation later. (Sun = 0, Mon = 1, Tues = 2, etc.)


field {Working_Day_Number}

We need to get number of days between start and end dates. (the output is in seconds, so /86400 to get days)


field {number_days}


DATETIME_DIFF({End},{Start})/86400

we will need to know the weekday number of the Start date


field {start_day_number}


DATETIME_FORMAT({start},'d')

Each weekday will occur every 7 days, so when we only look at the number of days leftover once we remove all the whole weeks from the total number of days, we want to know if the weekday of interest will occur in that remainder number of days

field {min_days}


ABS({start_day_number}-{Working_Day_Number}

field {remainder_day}


IF({min_days}<MOD({number_days},7),1,0)

Then some final logic

field {Total Work Days}


IF({start_Day_number}={working_day_number},ROUNDUP({number_days}/7,0),ROUNDDOWN(number_days/7,0)+remainder_days)

Seems to work as seen here:

This can definitely be consolidated to fewer cells, but for easier understanding it separated in multiple fields

Something additional will be needed in order to use the weekday name in place of the weekday number.

this may help with back formatting to a weekday name

Supported format specifiers for DATETIME_FORMAT

The DATETIME_FORMAT function will allow you to reformat the data from the date-type field into a string of your specifications. This is written in the form "DATETIME_FORMAT(Datetime, 'format s...