iflossdaily is right about the additional inactive reserve for 4 years. If you want you can sign on for an additional 2 years after your first 4 (that's 6 years active), and then your obligation is complete (no inactive). They do offer a 1 year AEGD, which ends up defering your obligation, so you still only have 4 years, but you don't start them until you finish your AEGD. In the mean time, you are getting your AEGD in a military clinic, so you are practically working for them anyway. The Army does offer really good health insurance and some other 'perks' (although I can't think of any right now, so they can't be that good!), so depending on your situation, you may end up saving money in the long run anyway.