How to use this calculator
It answers one question: given this payment, when does the balance hit zero, and what did the interest cost along the way? The extra-payment box repeats the calculation with a larger payment.
- Enter the current balance, not the original loan amount. Statements list both and they are very different numbers.
- Enter the interest rate from the statement. A federal loan may have several loans at different rates; run them one at a time rather than averaging.
- Enter the payment you actually make each month, including any autopay discount already applied.
- Add an extra amount to see the effect. The page reports both scenarios side by side.
- Check the first-month interest figure it shows against your statement. If they disagree, the rate or the balance is off.
A worked example: $30,000 at 6.5%
The first month's interest is $30,000 × 0.065 ÷ 12, which is $162.50. Any payment below that does not reduce the balance at all, which is the trap the tool flags directly.
| Payment | Time to pay off | Total interest |
|---|
| $350 | about 9.6 years | $10,439 |
| $450 | about 6.9 years | $7,321 |
One hundred dollars a month cuts nearly three years off the loan and saves about $3,118 of interest. On a ten-year horizon that is the best guaranteed return most people will be offered, and it comes with no market risk.
Notice the asymmetry: a 29% increase in the payment produces a 28% cut in the payoff time and a 30% cut in interest, because every extra dollar goes straight to principal while the scheduled payment is mostly servicing the balance.
What your results mean
The payoff date is a projection, not a promise. It assumes the rate never changes, the payment is made every month, and nothing new is borrowed. A single missed payment or a period of deferment moves the date.
Total interest is the cost of the schedule. On the example above, $350 a month costs more than a third of the original balance in interest, which is the argument for paying more when the budget allows.
This model is wrong for income-driven repayment, where the payment is a share of your income, the term is fixed at twenty or twenty-five years, and any remaining balance may be forgiven — with tax consequences this page cannot calculate. For those plans, use your servicer's calculator and read the forgiveness rules.
It is also wrong for a loan in a grace period or deferment, when interest may be accruing but no payment is due. Check the loan status before treating the date as real.
Frequently asked questions
Why does my payment barely dent the balance?
Because most of it is interest. At 6.5% on $30,000, the first $162.50 of every payment is interest and only what remains touches the principal. As the balance falls, that split improves on its own.
What happens if I pay less than the interest?
The balance grows. The calculator reports that the loan never pays off, which is accurate rather than pessimistic. That situation needs a larger payment or a different repayment plan.
Are extra payments applied to principal?
On most federal and private loans, yes, when you designate them as extra. Confirm with the servicer, because some apply overpayments to future scheduled payments by default, which saves nothing.
Should I pay extra or invest?
Paying extra earns a guaranteed return equal to the interest rate. Investing may earn more and may lose money. At a high rate the guaranteed saving is usually the stronger choice; at a low rate the comparison is closer.
Does refinancing help?
It can, if the new rate is meaningfully lower. It can also cost you federal protections such as income-driven repayment and forgiveness, which is a trade a lower rate does not always justify.
What if I have several loans?
Run each one here to see its own timeline, then use the debt payoff planner to decide the order of attack. Avalanche targets the highest rate, which is usually the right call for interest.
Sources & references
The payoff length is the standard logarithm of a fixed payment. Federal repayment plans are not.
Last updated: November 2, 2026. Reviewed by David Liu. Fixed-rate, single-balance loans with a constant payment.