Normal calculations for interest would be as the interest amount goes down the principal goes up. Not with Nelnet each payment you make, one month the principal goes up and the next month the principal goes down. There is no mathematical way to figure out what they doing . Examples principal interest 41.53 51.65 50.66 42.52 58.28 34.90 52.83 40.35 46.04 47 14 read full review »