It's got an awesome appetite: Tyrannosaurus Debt

How do you figure out daily interest from an APR on student loans due monthly? I have about 100k USD in student loan debt, at a fixed APR of 5.75%. I wanted to work out what the monthly rate was, but my debt holder tells me that the interest is actually calculated daily, though the payments are due monthly. Then they sent me twenty pages of amortization tables, I suppose imagining that it would help me somehow. Aside from seeing that 75-80% of each month's payment goes to interest before any of it goes to principal, the tables don't help me. I accrue and pay off a small amount of credit card debt each month, mostly in grocery bills. This is deliberate, since it's a monthly expense I'd have anyway, and paying by credit instead of debit is (I think) at least a slight help to my credit score. I have no other debt. I can see conceptually that paying as much extra as possible as soon as possible is best for reducing the total amount paid on this debt. What I'd like is to work all of this out into a big spreadsheet so that I can see the actual final result of any extra payments made. How do I do this? I feel like maybe I'm venturing into the realm of deep magic. I've poked around in the archives here and not found another question asking this; if I've missed it, a pointer would be great.