Function to detrmine start and end of month

Hello everybody
I need your help to make this function work

Function NewMonth(sdate As Date)
    If sdate >= CDate(DateSerial(Year(sdate), 12, 17)) And CDate(sdate <= DateSerial(Year(sdate), 1, 16)) Then
        NewMonth = "January"
    End If
End Function

I tested it but I got no result
I want to check a date in a cell and if this date is greater than 17 Dec. and less than 16 Jan. the result should be "January"