...and to simplify formula...

Sub DateCalc()
Dim LastMon, LastDay, CurYear
Dim ldtStart, ldtEnd
CurYear = Year(Now)
LastMon = Month(Now) - 1
ldtStart = Format(DateSerial(CurYear, LastMon, 1), "MM/DD/YYYY")
ldtEnd = Format(DateSerial(CurYear, LastMon + 1, 1) - 1, "MM/DD/YYYY")
MsgBox ldtStart & Chr(13) & ldtEnd
End Sub

OR...

Sub DateCalc()
Dim ldtStart, ldtEnd
ldtStart = Format(DateSerial(Year(Now), Month(Now) - 1, 1), "MM/DD/YYYY")
ldtEnd = Format(DateSerial(Year(Now), Month(Now), 1) - 1, "MM/DD/YYYY")
MsgBox ldtStart & Chr(13) & ldtEnd
End Sub