Swift: Get 30 days before 'Specific Date' [duplicate]

Question

I have a problem about showing specific date. Here the case, I have a random date from my API (06/16/2015) that always change. I put it into variable name toDate with Date type. I need to get 30 days before the toDate for my fromDate variable.

I read this but it's still not working. Note: I don't have any DatePicker in this controller.