Most loan calculators start with a term and give you a payment. Real life often runs the other way: you know what you can afford each month and want to know when the debt will be gone. This loan repayment calculator takes your balance, rate and payment, and works out the number of months, the debt-free date and the interest it will cost — plus how much faster you could finish by paying a little more.
How to use the loan repayment calculator
- Enter your current loan balance.
- Enter the interest rate (APR) shown on your statement.
- Enter the monthly payment you plan to make.
- Optionally add your next payment date to see the exact month you will be debt-free.
- Review the comparison tables: one shows the effect of paying $25 to $200 more, the other shows the payment needed to finish in one to five years.
Repayment time formula
Setting the loan balance equal to the present value of the payments and solving for the number of payments gives:
B is the balance, r the monthly rate (APR ÷ 12) and M the monthly payment. The term inside the logarithm, Br ÷ M, is the share of your first payment eaten by interest. If it reaches 1, the logarithm is undefined — your payment only covers interest and the loan never ends.
Worked example
You owe $15,000 at 9% and can pay $350 a month.
r = 0.09 ÷ 12 = 0.0075; first month's interest = 15,000 × 0.0075 = $112.50, or 32.1% of the payment.
n = −ln(1 − 0.321429) ÷ ln(1.0075) = 51.9 → 52 payments, or 4 years and 4 months.
The final payment is $313.62, and total interest comes to $3,163.62.
Small increases, big differences
Because extra money goes straight to principal, modest increases cut the term noticeably:
| Monthly payment | Time to repay | Interest saved |
|---|---|---|
| $350 | 4 years, 4 months | — |
| $400 | 3 years, 9 months | $484.53 |
| $450 | 3 years, 3 months | $837.63 |
| $550 | 2 years, 7 months | $1,318.57 |
Working backward, being debt-free in exactly three years would take $477.00 a month, and in two years $685.27.
Where to find extra money
Rounding up to the next $50, sending part of a raise or tax refund, or switching to half-payments every two weeks all add principal without much pain. Check first that the loan has no prepayment penalty and ask the servicer to apply extra amounts to principal.
Repaying several debts
If you have more than one loan, list them and decide on an order. The avalanche method sends extra money to the highest-rate debt first and minimizes total interest. The snowball method targets the smallest balance first for quicker wins. Either way, keep making at least the required payment on every account. For revolving balances with minimum payments, the credit card payoff calculator is a better fit; for a mortgage, use the mortgage payoff calculator.
Estimates only. The calculation assumes a fixed rate, payments on time each month and no new borrowing or fees.
Frequently asked questions
How do I calculate how long it will take to pay off a loan?
Use n = −ln(1 − B × r ÷ M) ÷ ln(1 + r), where B is the balance, r is the monthly rate and M is the monthly payment. Round the result up to whole months; the final payment will be smaller than the rest. A $15,000 balance at 9% paid at $350 a month takes 52 payments.
What is the smallest payment that will ever pay off the loan?
The payment must be larger than the interest charged each month, which is the balance times the monthly rate. At $15,000 and 9%, the first month's interest is $112.50, so any payment at or below that amount leaves the balance unchanged or growing.
How much does paying an extra $50 a month save?
On a $15,000, 9% loan paid at $350 a month, adding $50 shortens repayment from 4 years 4 months to 3 years 9 months and saves $484.53 of interest. The calculator's comparison table shows several increases side by side.
Is this the same as my lender's payoff schedule?
It is close but not identical. Many lenders accrue interest daily and apply payments on the date they arrive, so paying early or late in the month shifts the numbers slightly. Use the calculator for planning and your statement for exact figures.