Student Loan Calculator

How this student loan calculator works

This calculator does two things. First, it shows your standard monthly payment — the fixed amount that pays off your balance plus interest over your chosen term, the same way the federal Standard Repayment Plan works on a 10-year (120-month) schedule. Second, and more usefully, it shows what happens when you pay a little extra each month.

The standard payment uses the standard loan amortization formula. With a balance P, a monthly interest rate r (your annual rate ÷ 12), and a term of n months:

M = P · r(1 + r)ⁿ / ((1 + r)ⁿ − 1)

For the extra-payment scenario, the calculator runs a month-by-month amortization: each month it adds interest (balance × r), subtracts your payment plus any extra, and repeats until the balance reaches zero — then totals the interest paid and counts the months saved.

The math behind extra payments is simple but powerful. Your loan accrues interest on the outstanding balance every month. When you pay more than the scheduled amount, the extra goes straight to principal, so the balance drops faster and less interest accrues in every month that follows. The result is a shorter payoff and a smaller total interest bill — often by thousands of dollars.

Standard vs. paying extra

On a $30,000 balance at 6% over the standard 10 years, the payment is about $333 a month and you'd pay roughly $9,970 in interest. Add just $100 a month and you pay the loan off almost three years early and save over $3,000 in interest. Because there is no prepayment penalty on federal student loans, every extra dollar works in your favor with no downside on the loan itself.

Key terms explained

Standard Repayment Plan. The default federal plan: fixed payments over 10 years. It costs more per month than longer or income-driven plans but pays the least total interest.

Principal vs. interest. Principal is the amount you borrowed; interest is the cost of borrowing it. Early in repayment, a large share of each payment goes to interest — which is exactly why extra principal payments early on save the most.

Extra payment. Any amount above your required payment. Tell your servicer to apply it to principal (not to "pay ahead" on the next bill) to get the full interest-saving effect.

What this calculator does not model

To stay clear and broadly accurate, this tool models a single fixed-rate loan on the standard schedule. It does not model income-driven repayment plans (IBR, PAYE, SAVE), loan forgiveness, interest capitalization after a grace period or deferment, or the differences between federal and private loans. Those depend heavily on your income, family size, and loan type. For decisions involving those programs, check the official details at studentaid.gov or speak with your loan servicer.

Deciding whether to throw extra money at loans or elsewhere? Run your real take-home pay to see what's affordable, and weigh high-rate debt against long-term retirement growth before committing.

Sources & methodology

Repayment plans, terms, and federal loan rules referenced here are based on official U.S. Department of Education guidance:

• U.S. Department of Education — Federal Student Aid: Student loan repayment plans
• Federal Student Aid: Standard Repayment Plan (10-year fixed schedule)
• Payment math follows the standard loan amortization formula shown above.

Changelog. June 2026 — added explicit amortization formula, author attribution, and source citations. June 2026 — initial publication.

Frequently asked questions