Add up every payment on a 10-year loan and the interest can rival a car payment stretched across a decade. This tool shows the standard monthly payment, the total interest that comes with it, and exactly how much of both disappear when you add extra principal.
This models a fixed rate over the full term. Refinancing, deferment or income-driven plans change the real math.
The calculator applies the standard amortization formula to your balance, rate and term to find the minimum monthly payment. It then totals interest across all payments. Enter an extra monthly amount and we run the payoff month by month, crediting every dollar above the minimum directly to principal, and report how much interest and how many months that removes.
These are the calculator's own numbers on its own default loan, not a rounded marketing figure.
| Figure | Amount |
|---|---|
| Loan balance | $35,000 |
| Interest rate | 6.5% |
| Term | 10 years |
| Standard monthly payment | $397 |
| Total interest, standard term | $12,690 |
| Extra payment scenario | +$100 a month |
| Interest saved | about $3,504 |
| Time saved | about 31 months (roughly 2.6 years) |
Run the defaults and the standard payment on a $35,000 loan at 6.5% over 10 years comes to $397 a month, with $12,690 in total interest across the full term. Add $100 a month in extra principal and the real payoff, calculated month by month rather than estimated, saves about $3,504 in interest and clears the loan roughly 31 months early.
Federal loans carry protections a private refinance gives up for good: income-driven repayment plans that cap payments against your earnings, deferment and forbearance options during hardship, and forgiveness programs tied to certain careers or repayment histories. None of that comes back once the loan is refinanced into a private one. Before locking in a new fixed rate, compare it against what you are paying now and check whether the new lender offers any hardship provisions at all, because most private refinance products offer none.
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The standard amortization formula divides your balance by a factor derived from the interest rate and number of payments so that the payment stays fixed while the interest-to-principal ratio shifts each month toward principal.
Yes. Extra payments reduce the outstanding principal immediately, which shrinks the interest charged the next month and every month after. The savings compound over time in a way that can meaningfully shorten the loan term.
The amortization math is identical. Federal loans have specific repayment plans, deferment options and forgiveness programs that private loans do not. Check your servicer for the terms that apply to your specific loan type.
No, it's an estimate.
