in full if the European patent application is withdrawn, refused or deemed to be withdrawn before the Examining Divisions have assumed responsibility; or
at a rate of 75% if the European patent application is withdrawn, refused or deemed to be withdrawn after the Examining Divisions have assumed responsibility but before substantive examination has begun. This applies in particular where the applicant does not respond to the search opinion on time (leading to the application being deemed to be withdrawn under Rule 70a(3) - see B-XI, 8), but does file on time either the request for examination according to Rule 70(1) (see C-II, 1) or confirmation that he wishes to proceed with the application according to Rule 70(2) (see C-II, 1.1). An applicant unsure whether substantive examination has begun and wanting to withdraw the application only if he will receive the 75% refund may make withdrawal contingent upon the refund ("conditional" withdrawal).
For more details see OJ EPO 2009, 542OJ EPO 2013, 153.