How to count only full months between two dates

How to count the number of FULL months between two dates? Below shown the two dates and the number of full months should be returned.


Start Date End Date number of full months
16-Apr-12 to 22-Oct-12 => 5
1-Apr-12 to 21-Apr-12 => 0
1-Apr-12 to 31-Mar-13 => 12
1-Apr-12 to 14-Sep-12 => 5
10-Jun-12 to 31-Mar-13 => 9
3-Sep-12 to 31-Mar-13 => 6
1-Apr-12 to 8-Oct-12 => 6
1-Apr-12 to 2-Sep-12 => 5