Calculating Business Days

Bob:
Further to my earlier comment:
The macro below will automatically find the end date you wanted, then adjust the date to not fall on a weekend or holiday.

For the purposes of the macro I created named ranges:
(see Figure 1 below)
Target = A2 - that is where you put desired number of workdays. I added this to the sheet so that you can change the number of workdays without changing the macro code.
Start = A3 - your start date
End = A4 - you can put any date there, the macro will adjust it to your burnout date.

Once you put your start date and number of workdays run the macro. If the resulting end date is not a workday, it will ask you if you want to adjust it.

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Sub FinalDate()

    DesiredDays = Range("Target").Value
    
    Range("A5").GoalSeek Goal:=DesiredDays, ChangingCell:=Range("End")
    Dim cl As Range
    Set cl = Range("End")
    If Weekday(cl) = vbSaturday Or Weekday(cl) = vbSunday Or Range("hd") = "Holiday" Then
    
        continue = MsgBox("End date is on weekend or holiday." & vbCr & "Adjust the date?", vbYesNo, "Adjust?")
        If continue = vbYes Then
            Do
                cl.Value = cl.Value - 1
            Loop While Weekday(cl) = vbSaturday Or Weekday(cl) = vbSunday Or Range("hd") = "Holiday"
        End If
    End If
End Sub

Bob:
An Excel formula may be a bit complicated for what you need, as there would need to be a circular reference between the end date and Holidays. But there is a way to get what you need:

Use one of the formulas Allen suggested, e.g., =NETWORKDAYS(A3,A4,Holidays) say in the cell A5. Put your start date in cell A3, and any date in cell A4.
Then use the a functionality of Excel called Goal Seek. (Data tab - Forecast Group - What-If-Analysis -Goal Seek). (see Figure 1 below) for what to enter in the fields.

Once you click OK you will get a solution. (see Figure 2 below)

Note that I have a range named Holidays in my spreadsheet, as Allen suggested.

There is a quirk in how the process operates, because the target date found may actually be on a weekend or on a holiday, which technically will be correct, but not necessarily what you want. See, the process uses an algorithm, that is similar to trial and error, and once it finds the date that satisfies the value in the target cell, it does not look any further. This can be relatively easily corrected by manually adjusting the date to an earlier date just before the weekend or holiday (it should result in the same number of workdays). To aid in it, you can format the end date to show the weekday, and add an indicator for holiday in a cell beside it. the formula for the latter could be:

=IF(ISNA(MATCH(A4,Holidays,0)),"Not Holiday","Holiday")

See the figures.

It is worth remembering that the workdays function doesn't count the start day, so if the starting day is today and the end day is tomorrow, it will only return 1 day not 2.

If you need to do this often, you can create a macro to automate both the Goal Seek and the date adjustment. I will post a macro suggestion separately.

If I have a start date, and know there are 42 workdays left for a worker, is there a formula that would tell be the burnout date taking into consideration of the weekend days?