Start-up casual, on the other hand, allows you to wear your jeans. You dress casually but you should still definitely be properly groomed.
If you are in doubt about what is appropriate, always go the more formal route.
Get Your Clothes Ready The Night Before
A final tip, you should spend the day of the actual interview, getting yourself mentally prepared. Make sure all physical preparation; ironing, polishing your shoes and whatnot is done the night before.