SELECT months_between('01-JAN-2012',
'01-JAN-2013') months_between,
add_months(to_date('12-APR-2013',
'DD-MON-YYYY'),
1) add_months
FROM dual;

SELECT months_between('01-JAN-2012',
'01-JAN-2013') months_between,
add_months(to_date('12-APR-2013',
'DD-MON-YYYY'),
1) add_months
FROM dual;