Enter your balance, interest rate, and term to see your monthly payment, total interest paid, and total amount repaid.
On the values this page opens with — $30,000 at 5.5% over ten years — the payment is $325.58 a month, and you repay $39,069.46 in total. $9,069.46 of that is interest, close to a third of what you originally borrowed.
The split inside that first payment is the part worth understanding. Of the $325.58, $137.50 is interest and only $188.08 reduces the balance. Interest is charged on whatever you still owe, so as the balance falls the interest share shrinks and the principal share grows — slowly at first, then quickly. This is why a loan barely seems to move in its first two years and then collapses in its last two, and why any extra payment made early is worth far more than the same payment made late.
Stretching the same $30,000 from ten years to fifteen drops the payment to $245.13 — a saving of $80.45 a month, which is real money if cash is tight.
It also raises total interest from $9,069.46 to $14,122.51. That extra five years costs $5,053.05. Put another way, the longer term buys you $80.45 of monthly breathing room at a price of about $28 a month in additional lifetime interest. Sometimes that is a trade worth making — a longer term with the option to overpay is a legitimate way to buy flexibility. It is only a bad deal if you take the longer term and then never overpay.
Adding just $100 a month to the standard payment on the same loan clears it in 7.2 years instead of 10 and cuts total interest by about $2,753. Nothing else in the calculation is that leveraged, because every extra dollar goes straight against principal and stops accruing interest immediately.
Two cautions before you do it. Check that overpayments are applied to principal rather than held as a credit against your next scheduled payment — servicers differ, and some need to be told in writing. And on US federal loans, weigh it against the alternative: money thrown at the balance is money not available for an emergency fund, and a federal loan you might have forgiven under an income-driven plan is the last debt you want to prepay.
This is a standard amortising loan: fixed rate, fixed term, level payment. It deliberately does not model income-driven repayment, where the payment is set by your income rather than your balance, interest can be subsidised, and the remaining balance may be forgiven after a set number of years. Under those plans the total-interest figure here is meaningless.
If you hold US federal loans, that distinction is now the whole game — SAVE, PAYE and ICR have been replaced by RAP, with hard deadlines in 2027 and 2028. Use the income-driven repayment calculator instead, and see our crossover study for where each plan becomes the cheaper choice across twenty household types.
Standard student loan payments use the same fixed amortization formula as any other installment loan: payment = balance × i ÷ (1 − (1 + i)−n), where i is the monthly interest rate (annual rate ÷ 12 ÷ 100) and n is the number of monthly payments. Each payment splits between interest on the remaining balance and principal, with the interest share shrinking and the principal share growing over the life of the loan.
No — the underlying amortization math is identical for both federal and private student loans once you know the balance, rate, and term. What differs is the protections available: federal loans offer options like income-driven repayment, deferment, and certain loan forgiveness programs that private loans typically don't provide. See the Student Loan Repayment Calculator to explore those federal-specific repayment options.
Extra payments go straight to principal, which cuts the total interest you'll pay and shortens the loan term, since interest only accrues on the remaining balance. Use the Debt Payoff Calculator to see exactly how extra monthly payments change your payoff timeline and total cost.
Rates vary by loan type, whether the loan is federal or private, and the specific year it was disbursed, so there isn't one universal number worth assuming here. Check studentaid.gov for current federal loan rates, or your private lender's actual offer, and plug that real number in above for an accurate result.
Worked example: a $30,000 loan at 5.5% over a 10-year term has a monthly payment of $325.58. Over 120 payments, total interest comes to $9,069.46, bringing the total amount repaid to $39,069.46.
Weighing income-driven repayment instead? The Income-Driven Repayment Calculator compares the new RAP plan against IBR using 2026 income brackets. Repayment rules changed on July 1, 2026 — read what the new RAP plan means for your payment. Still costing out the degree itself? See the College Cost Calculator. The same ground is covered chapter by chapter in our book, From Paycheck to Portfolio.