Update, Not Restart
The extra-payment box is not grading your budget. It is an optional what-if.
This is the Loan Payoff Calculator with Extra Payments.
Add an optional extra each month or a one-time payment, then compare the estimated payoff date and interest with your current plan. You can change the numbers. Nothing here is a dare.
How this calculator works
- Both plans use the same monthly math: interest = balance × APR ÷ 12, rounded to the cent, then the payment.
- Extra money goes straight to principal, which lowers next month's interest.
- A one-time payment is added in the month you choose.
- Check that your lender applies extra payments to principal and charges no prepayment fee.
Results are estimates for planning, based only on the numbers you enter. Your lender's statement is the final word. See the full methodology and how we test the math.
How extra payments shorten a loan
Each month, part of your payment covers that month’s interest and the rest reduces the balance (the principal). An extra payment goes entirely to principal, if your lender applies it that way. The balance is then lower next month, so less interest is charged, and more of every later payment goes to principal. That’s why a modest extra amount can take months off a loan.
A worked example
Take the starting numbers in the calculator: an $18,000 loan at 7.9% APR with a $365 monthly payment.
- Current plan: paid off in 60 months, with $3,835.06 in interest.
- With $100 extra each month: paid off in 45 months, with $2,845.50 in interest.
The extra $100 a month saves $989.56 and finishes 15 months sooner. You can also try a one-time payment, such as a tax refund or a bonus, and choose the month it’s paid.
Works for car, student and personal loans
The math is the same for any fixed-rate loan with a monthly payment. Use your loan’s current balance (not the original amount), its APR and your exact monthly payment from your statement.
- Car loans: some auto loans calculate interest daily or precompute it, which changes how much an extra payment saves. Check your contract or ask your lender.
- Student loans: federal and private loans follow different rules. On federal Direct Loans, a payment goes to any fees or collection costs first, then to interest, then to principal (on Income-Based Repayment, interest comes before fees). There’s no prepayment penalty. If an extra payment equals or exceeds your monthly payment, your servicer moves your next due date forward unless you ask it not to, and interest keeps building while you’re paid ahead. Private lenders set their own rules; your servicer or lender can tell you how your payments are applied.
- Personal loans: check for a prepayment penalty before paying extra.
Things to check before sending extra money
- How your lender applies extra payments. Some let you mark them “principal only”; federal student loans apply payments to interest first.
- Whether there’s a prepayment fee.
- That your regular payment still goes out on time. Extra payments usually come on top of it.
Comparing debts?
If you’re paying a loan and credit cards at the same time, the higher-APR debt usually costs more each month. The snowball vs avalanche calculator shows which order clears everything sooner or for less interest. For a single card, use the credit card payoff calculator.
What this calculator assumes
Interest is charged monthly at APR ÷ 12 and rounded to the cent. Payments come at the end of each month, the rate is fixed, there are no fees, and extra money goes straight to principal. Your lender’s numbers may differ slightly. The results are estimates; your statements are the final word. See the full methodology and our disclaimer.
Keep every debt in one plan
The Debt Payoff Planner Pro spreadsheet lists this loan alongside your cards, maps the payoff order and logs the payments you actually make.