Quick answer
This calculator shows how extra payments change a student loan's payoff date and total interest. A $37,000 loan at 6.5% paid at $400 a month clears in 129 months with $14,479 of interest. Adding $100 a month clears it in 95 months instead and saves $4,070 of interest — 34 fewer payments for $9,500 of extra contributions.
How the Student Loan Payoff works, step by step
Enter your balance, interest rate, current monthly payment and any extra amount you can add. The calculator amortises the loan month by month: interest on the balance first, the rest of the payment to principal, then repeats on the smaller balance. It runs the base payment and the payment-plus-extra side by side, so the months and dollars saved are exact, not estimated.
Know your rate's context. Federal Direct Loans first disbursed between July 1, 2026 and June 30, 2027 carry a fixed 6.52% for undergraduates, 8.07% for graduate and professional students, and 9.07% for PLUS loans, per Federal Student Aid. The rate is fixed for the life of each loan and set annually from the May 10-year Treasury auction — the tool's 6.5% default sits almost exactly on the current undergraduate rate.
Extra payments go entirely to principal, which is why they punch above their weight: each extra dollar removes the interest that dollar would have attracted for the rest of the term. Confirm your servicer applies extra payments to principal rather than as advance payments on future bills — the two treatments look identical on a statement but only the first shortens the loan.
Check your payment against the standard plan. The standard 10-year payment on $37,000 at 6.5% is $420.13 a month, with $13,415 of interest over the term. A $400 payment is below that standard figure, which is why the base case runs 129 months instead of 120 — the calculator exposes a payment that is quietly too small, as well as one that is generous.
Compare the saving against your alternatives honestly. At 6.5%, an extra dollar earns a guaranteed 6.5% by avoiding interest. That beats a savings account and carries no market risk, but it is below the long-run return investors hope for from equities — and unlike an investment, a paid-off loan cannot be re-borrowed in an emergency, so keep your cash buffer intact first.
The formula
Monthly payment = Balance × (r ÷ 12) ÷ [1 − (1 + r ÷ 12)^(−months)]. Total interest = (payment × months) − balance. Extra payments shorten the month count in the month-by-month simulation.
Worked example — try it on the calculator above
Worked example: $37,000 at 6.5%, $400 a month plus $100 extra
Month one: interest is $37,000 × 6.5% ÷ 12, about $200, so $200 of the $400 payment reduces principal. At $400 a month the balance clears in month 129 — 10 years and 9 months — with total interest of $14,479. Pay $500 instead and the balance clears in month 95, just under 8 years, with $10,410 of interest. The extra $100 a month, $9,500 in total, removes $4,070 of interest and 34 payments. The standard 10-year payment on this loan would be $420.13, so even the $500 payment is only $80 above standard — a modest overpayment with a large effect.
Frequently Asked Questions
What is the standard federal student loan repayment term?
10 years on the Standard Repayment Plan, with a minimum payment of $50. Federal undergraduate loans disbursed in 2026-27 carry a fixed 6.52% rate; graduate loans 8.07% and PLUS loans 9.07%. Rates are set each year from the Treasury auction and fixed for the life of each loan.
Should I pay extra or use an income-driven plan?
They solve different problems. Income-driven repayment caps payments at a share of income and forgives any balance after a set period, but total interest paid is usually higher. If you can afford the standard payment comfortably, extra payments cost less overall. Federal repayment options changed under the 2025 tax law — verify the current plans at studentaid.gov before choosing.
Does paying extra on student loans affect my taxes?
Up to $2,500 of student loan interest a year is deductible as an adjustment to income, without itemising. For 2026 it phases out between $85,000 and $100,000 of modified AGI for single filers ($175,000 to $205,000 joint). Paying the loan off faster reduces the interest you can deduct, but a dollar of interest saved beats the roughly 22 cents of tax it might have saved in the 22% bracket.
Should I pay off student loans before investing?
After capturing any employer retirement match and holding a starter emergency fund, compare rates. Above roughly 7%, paying the loan down is hard to beat on a risk-adjusted basis. At 4% to 5%, investing the surplus is defensible, especially inside tax-advantaged accounts whose annual contribution room expires.
Estimates, not advice. This calculator provides educational estimates based on the inputs you enter and the assumptions shown on this page. It is not financial, tax or investment advice, and it cannot see your full situation. Verify important figures against official sources, and consider a qualified professional for decisions about your own money. See our Disclaimer and Methodology.