My spouse has a UK student loan. The loan has a 1.5% interest rate, and you only start repayments once you earn over a certain threshold. They do a calculation of how much you need to repay which I believe is 9% of what you earn over that threshold, so the repayment amount varies as your salary changes over time. The loan has no term—you just make repayments until it’s repaid, or until you reach an age when it is automatically discharged.
So…does anybody have any idea how to calculate how much of what we repaid in 2018 went towards interest for the purposes of the federal student loan deduction? The Student Loan Company just provides a statement of the monthly repayments and the new interest each month, with no indication of how much went towards repaying principal/interest. All my Googling just throws up how to calculate figures for a fixed-term loan like a mortgage or car loan with a known amortization schedule. Is there even a concept of splitting repayment amounts between principal and interest for such a loan?
Any advice would be a huge help!