<p>This ultimately is a very simple or very complicated question, and which of those it is largely depends on the intent behind the question.</p>
<p>The simple answer (and the one that applies to the overwhelming majority of mids) is that when you start 2/C year classes, you're agreeing to another 2 years at USNA and another 5 upon graduation.</p>
<p>The complicated answer is that the actual moment your obligation starts at USNA and beyond, the "penalties" for leaving early, and the ultimate number of years you'll devote to the USN or USMC are a bit more complex and, in some cases, may vary based on a variety of factors. </p>
<p>Your USNA commitment may start at noon the first day of classes or the moment you sign the paperwork or some other time -- I must confess that I don't know (and I'm a BGO) the exact moment. And, frankly, the exact moment doesn't matter for counseling prospective candidates because, in no case, will it occur for well over two years. </p>
<p>If you're a mid who is thinking of quitting after 2 years, you will hopefully notify your chain of command and they typically (at least in my experience) will ensure you don't "accidentally" commit yourself until you have affirmatively made the decision to do so (i.e., they will hold you out of classes for a few days, etc.). There is no interest in "tricking" people into a commitment, although the decision-making process can't go on forever.</p>
<p>If you do decide to stay at USNA and, for some reason (academics, fitness, honor, etc.) don't make it through the final two years, you may have either to pay back some/all of the cost of your education and/or serve as an enlisted sailor for a period of time. I'm sure there are laws on the issue but, in practice (at least in my day), what happened to you had a lot to do with the circumstances that led to your departure. In any event, those ramifications will be made clear to you at the time. I have heard that the USN is getting tougher on recouping costs, etc. </p>
<p>Finally, your obligation to the USN or USMC will typically be at least 5 years (and there are some very rare exceptions to that) or may be longer than 5 years, depending on your service selection. You will fully understand your service obligation when you make your choice (and, presumably, before). Again, for the overwhelming majority of mids, your obligation starts upon graduation. For some mids, it may start at a later date; again, if you are in this category, you will be advised about this. </p>
<p>So, back to the initial question -- MORE OR LESS, when you start 2/C year classes, you are agreeing to spend another 2 yrs at USNA and another 5 years as an officer. That should be sufficient information for 99% of candidates. Not to say the minutiae isn't important but, for candidates who haven't even been appointed, it really isn't (or shouldn't be).</p>