Iirc, student loans are simple interest loans.
Google tells me the formula for a simple interest loan is: I (interest) = P (principal) x r (rate) x t (time periods). It also tells me the "average" student loan interest rate is: "For the 2017-2018 school year, the fixed rate on undergraduate Direct loans (subsidized and unsubsidized) is 4.45%. The rate for graduate or professional Direct unsubsidized loans is 6.00%. Direct PLUS loans have an interest rate of 7.00%. However, that doesn't mean all your debt has the same interest rate."
As you all know, Im not so good at math. Can one of you pump those numbers through the formula and let me know if its accurate?