UCAS Application when transferring universities

I wish to to resit alevels this summer to get the requirements for other unis so I can transfer. In UCAS what should I write for the start and end date of the university I am currently in?

when did you start? thats the start date
when would you leave if you got an offer you would like to accept? that's the end date

Don't forget you'll need to add the exam centre you'll resit your A levels at - do you have a plan for if the A level exams and your university exams clash?