Student Loan Calculator
Calculate your monthly student loan payment, the total interest over the repayment term, and exactly how much time and money extra payments save — for federal or private loans.
Written by Daniel Mercer, CFP® · Reviewed by Sarah Lindqvist, CFA
Last reviewed:
Monthly payment
$397.95
- Payoff time
- 10 yr
- Total interest
- $12,754
- Total repaid
- $47,754
Balance over time
What this calculator does
Student debt is the loan people carry longest without ever seeing its full arithmetic. This calculator lays it out: the monthly payment for any balance, rate, and term; the total interest the schedule implies; and — the part worth staring at — what a modest extra payment does to both. The chart draws the balance falling under the standard payment and under your payment-plus-extra, so the years you’d claw back are visible, not hypothetical.
How the math works
Standard repayment uses the amortization formula:
M = P · r(1 + r)ⁿ / ((1 + r)ⁿ − 1)
with P the balance, r the monthly rate, n the number of payments. Each month interest accrues on the remaining balance; the payment covers interest first, principal second. Extra payments skip the interest line entirely and hit principal — which is why their effect compounds over the remaining life of the loan.
A worked example
A $35,000 balance at 6.53% (a recent federal undergraduate rate) on the 10-year standard plan:
- Payment: $397.97 per month
- Total interest: about $12,760
- Total repaid: about $47,760
Add $100 extra each month: the loan finishes in about 7 years 5 months instead of 10, and total interest falls to roughly $9,220 — saving about $3,500 and 31 months. The extra $100 isn’t gone, either; it’s forced savings earning a guaranteed 6.53% return, which is more than most bonds pay.
Practical tips
- Attack loans, not the loan. Most graduates hold several federal loans at different rates. Extra payments do the most damage pointed at the highest-rate loan first (the avalanche logic — compare strategies in the debt snowball calculator).
- Beware the consolidation trade. Consolidating simplifies paperwork, but choosing a longer term at the weighted-average rate can add tens of thousands in interest. Run the old and new terms here before signing anything.
- Think twice before refinancing federal loans privately. A private refinance may cut the rate, but it permanently surrenders federal protections — income-driven plans, deferment, forbearance, and any future forgiveness. Price the savings here, then weigh them against the insurance you’re giving up.
- Keep paying through the grace period if you can. Interest on unsubsidized loans accrues from disbursement. Payments made before capitalization events reduce the principal that future interest is calculated on — small early dollars outperform larger later ones.
The term is the biggest lever
Rates get the headlines, but the term quietly controls the total. This same $35,000 at 6.53% costs about $12,760 in interest over 10 years — and roughly $36,000 over 25 years on an extended plan, for a payment only about $161 lower. When a longer term is the only way to make the budget work, that’s a legitimate trade; the point of running the numbers is making it a chosen trade. Once your payment has room to spare, the loan payoff calculator shows what each additional $50 does to any loan you’re stuck with.
Frequently asked questions
- What repayment term should I enter for federal loans?
- The federal Standard Repayment Plan is 10 years, which is also the default this calculator loads. Consolidation and extended plans stretch to 20–30 years — lower payments, far more interest. Income-driven plans (like IBR or the current income-based options) recalculate payments annually from your income, which fixed-payment math can't model; use your servicer's estimates for those.
- Should I pay off student loans early or invest?
- Compare the loan's rate to a realistic after-tax investment return. Extra payments on a 6.5% loan earn a guaranteed 6.5%; historically stocks have returned more on average but with real risk. Many planners split the difference: capture any employer 401(k) match first (an instant 50–100% return), then attack loans above ~6%, then invest. Whatever you choose, this calculator prices the loan side of the decision.
- How does student loan interest actually accrue?
- Federal loans use simple daily interest on the outstanding principal: balance × (rate ÷ 365) per day. Unpaid interest doesn't compound monthly while you're in normal repayment, but it capitalizes (gets added to principal) at specific events — like leaving deferment. This calculator's monthly model matches standard repayment behavior closely for planning purposes.
- Do extra payments work the same as with other loans?
- Yes, with one important instruction: tell your servicer to apply extra amounts to the current balance as principal, not to "advance the due date". Also specify which loan in a group gets the extra — target the highest rate. Federal loans never have prepayment penalties; private loans almost never do.
- Is student loan interest tax-deductible?
- Up to $2,500 of student loan interest per year is deductible as an above-the-line deduction, subject to income phase-outs set by the IRS. That effectively discounts your interest rate a little in the years you qualify — worth knowing, but rarely enough to change the payoff-versus-invest decision by itself.
Sources
Written by
Daniel is a Certified Financial Planner™ with 12 years of experience helping households manage debt, savings, and retirement planning. He writes ToolGrym’s calculator guides and explains the math behind every tool.
Reviewed by
Sarah is a CFA charterholder who reviews every ToolGrym calculator and article for mathematical accuracy. She has 10 years of experience in fixed-income analytics and consumer lending models.