I know of course no one can sit here and tell me for definite, but what are the odds ? My period started on the 4th August and it said my fertile window is between the 12th-19th August. Me and my partner had unprotected sex on the 9th, 12th, 13th ,14th and are planning on for the rest of the week . I'm 18 and healthy and he's 19 and also healthy