If your interviewer is going to realise at some point during the interview that you have a stutter anyway then I think disclosing the fact before you begin is the better option. At least this way: 1. You might have some peace of mind that you may not feel the need to hide your stutter (if you usually do so). 2. They might be able to make some alterations to the interview, ie. give you more time or unlimited time per question. 3. They may see the stutter as what it actually is rather than assuming you're nervous or unprepared.