Hi Amit,
First of all using only Datediff you won't be getting the exact month count as per your convenient.
Reason : Datediff will just return the number of Month boundaries that have been passed.
If you want month count should be returned as per exact days elapsed,try below query.
declare @startdate datetime
declare @enddate datetime
set @startdate='31-March-2014'
set @enddate='01-June-2014'
select case
when @startdate > @enddate then NULL
when DATEPART(day,@startdate) > DATEPART(day,@enddate) then DATEDIFF(month,@startdate,@enddate)-1
else DATEDIFF(month,@startdate,@enddate) end as Count_of_month
:-)