Student Loan Payoff Calculator (Extra Payment vs Term)
Student loans with a fixed rate amortize like any installment loan. This page computes the scheduled payment, then adds an extra amount you choose each period and shows the new payoff time and interest saved. Forgiveness, income-driven plans, and subsidies are not modeled.
Scheduled payment333.06
Payment with extra433.06
Payoff time (months, with extra)85.3
Months saved34.7
Interest on schedule9,967.38
Interest with extra6,920.89
Interest saved3,046.49
How this calculation works
Standard payment uses the amortization formula: P × r / (1 − (1+r)^−N), with r = annual rate ÷ payments per year and N = years × payments per year.
New payment = standard + extra. Periods to payoff = ln(pmt / (pmt − rP)) / ln(1+r) when the payment covers interest.
Interest originally ≈ payment × N − principal. With extra, interest ≈ new payment × new periods − principal. The difference is interest saved.
Extra payment is treated as extra principal each period, not a one-off. Set extra to 0 to see the scheduled loan only.
Worked example
₩30,000 (or 30,000 currency units) at 6% for 10 years monthly is about 333.06 per month. Adding 100 extra raises the payment to 433.06 and cuts both term and total interest.
Frequently asked questions
Is this only for student loans?
The math is any fixed-rate amortizing loan. The label is for search; car and personal loans work the same if fees are ignored.
What about income-driven repayment?
IDR payments follow income and can extend the term. This tool is standard amortization plus extra. It will not cap payment at a percent of discretionary income.
Does extra go to principal?
We assume the servicer applies extra to principal after interest, the usual instructed extra-principal path. Confirm with your servicer.
Why is the last period a fraction?
Closed-form payoff is not always a whole number of months. Treat it as an estimate; the final bill is a smaller leftover payment.
0% interest?
Payment is principal ÷ number of periods. Extra still shortens the calendar by paying more of the balance each time.