Why is datediff interval "weekday" returning interval based on weeks and not days minus weekends?

Question

I'm using the expression builder to give me a calculated value. It looks like this:

=DateDiff("w",Date(),[Latest_Call_Date])

However, this is giving me results as if it were doing a calculation based on weeks instead of days minus weekends . When I try the same function, but with the interval set to days (d) instead of weekdays (w) I get the expected results (but of course, including Saturdays and Sundays, which I do not wish to include in the calculation). So, for example, for everyday this week I'm getting 1,2,3,4,5 day differences but they all return zero with weekdays. That formula is:

=DateDiff("d",Date(),[Latest_Call_Date])

Is there something else I have to do to get "weekdays" interval to work?

I'm using Access 2013, in an .accdb file format.

Answer 1

Weekdays excluding weekends (and holidays) are usually labelled workdays.

DateDiff("w", ..) returns the count of a weekday between two dates, while

DateDiff("ww", ..) returns the difference in calendar weeks between two dates.

Counting workdays takes a little more. This function will do:

Public Function DateDiffWorkdays( _
    ByVal datDate1 As Date, _
    ByVal datDate2 As Date, _
    Optional ByVal booWorkOnHolidays As Boolean) _
    As Long

'   Calculates the count of workdays between datDate1 and datDate2.
'   2014-10-03. Cactus Data ApS, CPH

    Dim aHolidays() As Date

    Dim lngDiff     As Long
    Dim lngSign     As Long
    Dim lngHoliday  As Long

    lngSign = Sgn(DateDiff("d", datDate1, datDate2))
    If lngSign <> 0 Then
        If booWorkOnHolidays = True Then
            ' Holidays are workdays.
        Else
            ' Retrieve array with holidays between datDate1 and datDate2.
            aHolidays = GetHolidays(datDate1, datDate2)
        End If

        Do Until DateDiff("d", datDate1, datDate2) = 0
            Select Case Weekday(datDate1)
                Case vbSaturday, vbSunday
                    ' Skip weekend.
                Case Else
                    ' Check for holidays to skip.
                    ' Ignore error when using LBound and UBound on an unassigned array.
                    On Error Resume Next
                    For lngHoliday = LBound(aHolidays) To UBound(aHolidays)
                        If Err.Number > 0 Then
                            ' No holidays between datDate1 and datDate2.
                        ElseIf DateDiff("d", datDate1, aHolidays(lngHoliday)) = 0 Then
                            ' This datDate1 hits a holiday.
                            ' Subtract one day before adding one after the loop.
                            lngDiff = lngDiff - lngSign
                            Exit For
                        End If
                    Next
                    On Error GoTo 0
                    lngDiff = lngDiff + lngSign
            End Select
            datDate1 = DateAdd("d", lngSign, datDate1)
        Loop
    End If

    DateDiffWorkdays = lngDiff

End Function

And the Holidays, should you need it some day:

Public Function GetHolidays( _
    ByVal datDate1 As Date, _
    ByVal datDate2 As Date, _
    Optional ByVal booDesc As Boolean) _
    As Date()

'   Finds the count of holidays between datDate1 and datDate2.
'   The holidays are returned as an array of dates.
'   DAO objects are declared static to speed up repeated calls with identical date parameters.
'   2014-10-03. Cactus Data ApS, CPH

    ' The table that holds the holidays.
    Const cstrTable             As String = "tblHoliday"
    ' The field of the table that holds the dates of the holidays.
    Const cstrField             As String = "HolidayDate"
    ' Constants for the arrays.
    Const clngDimRecordCount    As Long = 2
    Const clngDimFieldOne       As Long = 0

    Static dbs              As DAO.Database
    Static rst              As DAO.Recordset

    Static datDate1Last     As Date
    Static datDate2Last     As Date

    Dim adatDays()  As Date
    Dim avarDays    As Variant

    Dim strSQL      As String
    Dim strDate1    As String
    Dim strDate2    As String
    Dim strOrder    As String
    Dim lngDays     As Long

    If DateDiff("d", datDate1, datDate1Last) <> 0 Or DateDiff("d", datDate2, datDate2Last) <> 0 Then
        ' datDate1 or datDate2 has changed since the last call.
        strDate1 = Format(datDate1, "\#yyyy\/mm\/dd\#")
        strDate2 = Format(datDate2, "\#yyyy\/mm\/dd\#")
        strOrder = Format(booDesc, "\A\s\c;\D\e\s\c")

        strSQL = "Select " & cstrField & " From " & cstrTable & " " & _
            "Where " & cstrField & " Between " & strDate1 & " And " & strDate2 & " " & _
            "Order By 1 " & strOrder

        Set dbs = CurrentDb
        Set rst = dbs.OpenRecordset(strSQL, dbOpenSnapshot)

        ' Save the current set of date parameters.
        datDate1Last = datDate1
        datDate2Last = datDate2
    End If

    lngDays = rst.RecordCount
    If lngDays = 0 Then
        ' Leave adatDays() as an unassigned array.
    Else
        ReDim adatDays(lngDays - 1)
        ' As repeated calls may happen, do a movefirst.
        rst.MoveFirst
        avarDays = rst.GetRows(lngDays)
        ' rst is now positioned at the last record.
        For lngDays = LBound(avarDays, clngDimRecordCount) To UBound(avarDays, clngDimRecordCount)
            adatDays(lngDays) = avarDays(clngDimFieldOne, lngDays)
        Next
    End If

    ' DAO objects are static.
    ' Set rst = Nothing
    ' Set dbs = Nothing

    GetHolidays = adatDays()

End Function