How Student Loan Interest Works
Student loan interest accrues daily based on the outstanding principal balance. The daily interest charge is: Principal Balance x (Annual Interest Rate / 365). On a standard 10-year repayment plan, the monthly payment is fixed using the standard amortization formula. In the early months, more of each payment covers interest; as the balance decreases, more reduces principal.
Federal vs. Private Student Loans
Federal student loans offer income-driven repayment plans, Public Service Loan Forgiveness (PSLF), deferment, and forbearance options that private loans typically do not. Exhaust all federal repayment options before refinancing to private loans -- refinancing removes access to federal protections permanently.
Standard vs. Income-Driven Repayment
The standard 10-year repayment plan produces the lowest total interest cost for federal loans. Income-driven repayment (IDR) plans cap monthly payments at a percentage of discretionary income and extend the repayment period, which reduces monthly payments but significantly increases total interest over time.
Paying Off Student Loans Faster
Even $50 to $100 extra per month applied to principal can shorten a 10-year loan by one to two years. Some borrowers use the avalanche method -- paying the highest-rate loan first -- to minimize total interest across multiple loans.
Loan Forgiveness Programs
Public Service Loan Forgiveness (PSLF) forgives remaining federal loan balances after 120 qualifying monthly payments (10 years) while working full-time for a qualifying government or nonprofit employer, under an income-driven repayment plan. Teacher Loan Forgiveness offers up to $17,500 for eligible teachers in low-income schools after five consecutive years of service. Both programs require enrollment in the correct repayment plan from the start -- payments made under an ineligible plan do not count retroactively.
Common Student Loan Mistakes
Refinancing federal loans to private before exhausting federal options. Refinancing permanently forfeits access to income-driven repayment, PSLF, and federal deferment or forbearance -- a decision that cannot be undone.
Not recertifying income annually for income-driven plans. Missing recertification can cause your payment to jump to the standard amount and unpaid interest to capitalize onto the balance.
Frequently Asked Questions
Does interest accrue while I'm in school? On subsidized federal loans, no -- the government pays interest while you're enrolled at least half-time. On unsubsidized federal loans and most private loans, interest accrues from disbursement even while you're in school.
What happens if I can't make a payment? Federal loans offer deferment and forbearance options that temporarily pause payments. Private lenders may offer hardship programs, but terms vary -- contact your servicer before missing a payment.
The Inputs, Field by Field
Loan balance. The total principal you currently owe on the loan you want to model. If you carry several loans at different rates, model them separately for accuracy, or enter a combined balance with your weighted-average rate for a quick overall picture.
Interest rate. The annual rate on the loan. Federal loan rates are fixed for the life of the loan and set each year by Congress; private student loan rates may be fixed or variable, so confirm which you have before relying on a single number.
Repayment term. The number of years over which you repay. Ten years is the federal standard and produces the lowest total interest; longer terms lower the monthly payment but increase total interest, as the standard-versus-income-driven comparison above shows.
Extra monthly payment. Any amount above the required payment, if your calculator supports it. Extra dollars go straight to principal, and even $50 to $100 a month can shave a year or more off a standard 10-year loan.
How to Read Your Results
The monthly payment is what a standard fixed schedule requires. The total interest figure is where repayment strategy matters most: stretching a federal loan onto a longer income-driven plan can multiply it, while extra principal payments shrink it. Check the payoff date against your career and life plans, and remember that on unsubsidized loans interest was likely accruing while you were in school, so your starting balance may already exceed what you originally borrowed.
Assumptions and Limitations
This calculator assumes a single fixed rate and equal monthly payments on a standard schedule. It does not model income-driven repayment formulas, loan forgiveness such as PSLF, interest subsidies on subsidized loans, or interest capitalization after deferment or forbearance -- each of which can change your real numbers substantially. Treat the output as an educational estimate, not repayment counseling. For federal-specific figures, your loan servicer and the official Federal Student Aid loan simulator are the authoritative sources.
Related Calculators and Guides
New to borrowing for school? Start with our guide to getting a student loan. To pay down a balance faster, read how to pay off a loan faster and model extra payments with the early payoff calculator. If you are weighing private refinancing, the refinance calculator shows the trade-off -- but refinancing a federal loan permanently forfeits federal protections.