Counting Month Ends

Kim has a worksheet into which she places a start date (column C) and an end date (column D). She needs a way to calculate the count of month ends between the two dates. For instance, if the start date is 1/1/17 and the end date is 7/31/17, the number of month ends is 7. If, however, the end date is 7/30/17, the number of month ends is 6.

There are any number of formulas you could devise to calculate the proper count. The simplest formula is if you can always count on the date in column C being the start of a month. In that case, the following formula will work just fine:

=DATEDIF(C1,D1+1,"m")

If you cannot count on column C containing a date that is the start of a month, but you can count on the beginning and ending dates always being in the same year, then any of the following formulas will do the trick:

=IF(MONTH(D1+1)=MONTH(D1),MONTH(D1)-MONTH(C1),MONTH(D1)-MONTH(C1)+1)
=IF(MONTH(D1+1)=MONTH(D1),MONTH(D1)-1,MONTH(D1))-MONTH(C1)+1
=MONTH(EOMONTH(D1,0))-MONTH(EOMONTH(C1,0))+(EOMONTH(D1,0)=D1)
=IF(EOMONTH(D1,0)=D1,MONTH(D1)-MONTH(C1)+1,MONTH(D1)-MONTH(C1))
=IF(D1<EOMONTH(D1,0),MONTH(D1)-1,MONTH(D1))-MONTH(C1)+1
=MONTH(D1)-MONTH(C1)+IF(D1=EOMONTH(D1,0),1,0)

If the years on the beginning and ending dates might be different, then the formulas are a bit more complex. Any of the following variations will calculate the correct number of month ends in the date range:

=12*(YEAR(D1)-YEAR(C1))+MONTH(D1)-MONTH(C1)+INT(D1=EOMONTH(D1,0))
=12*(YEAR(D1)-YEAR(C1))+MONTH(D1)-MONTH(C1)+IF(EOMONTH(D1,0)=D1,1,0)
=12*YEAR(D1)+MONTH(D1)-12*YEAR(C1)-MONTH(C1)+IF(D1=EOMONTH(D1,0),1,0)
=12*YEAR(D1)+MONTH(D1)-12*YEAR(C1)-MONTH(C1)+(D1=EOMONTH(D1,0))
=12*YEAR(D1)+MONTH(D1)-12*YEAR(C1)-MONTH(C1)+(DAY(D1+1)=1)
=MONTH(D1)+12*YEAR(D1)-MONTH(C1)-12*YEAR(C1)+IF(EOMONTH(D1,0)=D1,1,0)
=(MONTH(D1+1)+12*YEAR(D1+1))-(MONTH(C1)+12*YEAR(C1))
=IF(D1=EOMONTH(D1,0),1,0)+MONTH(D1)-MONTH(C1)+((YEAR(D1)-YEAR(C1))*12)
=IF(EOMONTH(D1,0)=D1,(MONTH(D1)-MONTH(C1)+1)+(YEAR(D1)-YEAR(C1))*12,MONTH(D1)-MONTH(C1)+(YEAR(D1)-YEAR(C1))*12)
=IF(D1=EOMONTH(D1,0),DATEDIF(EOMONTH(C1,-1),EOMONTH(D1,0),"m"),DATEDIF(EOMONTH(C1,-1),EOMONTH(D1,0),"m")-1)
=IF(D1<C1,"Error",MONTH(D1)-MONTH(C1)+IF(D1MONTH(D1+1))*1)
=IF(D1<C1,"Error",(YEAR(D1)-YEAR(C1))*12+(MONTH(D1)-MONTH(C1))+(EOMONTH(D1,0)=D1))
=SUM(N(FREQUENCY(EOMONTH(ROW(INDIRECT(C1&":"&D1)),0),EOMONTH(ROW(INDIRECT(C1&":"&D1)),0))>0))-(D1<EOMONTH(D1,0))

Some of these formulas are a bit long, so you'll want to carefully watch that you get them all if you choose to use one.

If you prefer to use a macro approach, then the following user-defined function may be of interest:

Function CountMonthEnds(sd As Date, ed As Date) As Integer
    Dim ceom As Integer
    Dim cmonth As Integer
    Dim lmonth As Integer
    Dim x As Date

    cmonth = 0
    ceom = 0
    cmonth = Month(sd)
    lmonth = cmonth
    ' go to end date + 1 to allow for end date being end of month
    For x = sd To ed + 1
        cmonth = Month(x)
        If cmonth <> lmonth Then
            ceom = ceom + 1
            lmonth = cmonth
        End If
    Next x
    CountMonthEnds = ceom
End Function

The macro simply steps through all the dates between the beginning and ending dates. It looks at the month for each of the dates, and if it changes, then it counts that as a "month end." This count is returned by the function.

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