Free tool — for anyone paying down a car, student or personal loan
Loan Extra-Payment Calculator
Put one loan in — balance, APR, monthly payment — add the extra you could pay each month, and this free spreadsheet shows when the loan is gone with and without that extra, the interest each way, and the difference. Every figure comes from a month-by-month schedule on its own tab, so you can see exactly where the savings come from. It opens pre-filled with a fictional auto loan: $9,800 at 7.4% with a $359 payment is gone in month 30 on the payment alone, and in month 23 with $100 a month on top — $224 less interest. No email, no signup, one click to download; it opens in Excel and LibreOffice, or in Google Sheets once you upload it to Google Drive.
Take it with you — free, no signup
Direct download. No email, no account — just the file.
What it does
- Takes one loan — balance, APR and your monthly payment, or the months left if you'd rather have the payment worked out for you — plus one monthly extra and the month it starts.
- Answers the question on one screen: the payoff month and date on the payment alone and with your extra, total interest each way, the interest you save, the months you save, and the total extra you put in.
- Shows the math on a 360-month schedule, side by side for both cases: the balance each month starts with, that month's interest, what you paid, and what was left.
- Warns you when a payment doesn't cover the first month's interest, so a loan that would never pay off doesn't quietly look like one that does.
- Comes pre-filled with a fictional auto loan, so the whole calculation is running before you type anything — replace the cream cells with the figures on your own statement.
- Reminds you to ask your lender to apply extra money to principal. Some lenders treat it as an early payment of next month's bill, which can save little or no interest.
- Uses plain monthly amortization — APR ÷ 12 on the balance you start the month with — so a loan that accrues interest daily, as some auto loans do, can differ by a few dollars a month.
Related reading
Own it, don't rent it
More than one loan, or extra money that doesn't arrive every month?
This free calculator runs one loan with one monthly extra. If you are paying down more than one loan, or your extra money doesn't arrive every month, the full Loan Payoff Calculator — Extra Payments is built for that. Put up to eight auto, student and personal loans in one file, and give each its own mix of extras: a monthly amount from the month you choose, one-time payments on the months they actually arrive (a tax refund, a bonus — up to thirty in all), and true bi-weekly payments modeled as 26 half-payments a year. It checks 0% promo plans against their end month and, for deferred-interest plans, prices the back-charged interest that lands if the balance isn't cleared in time. It runs one shared extra budget through three payoff orders — highest rate first, smallest balance first, and your own — month by month, with each paid-off loan's payment rolled into the next in its own column, and compares total interest, the debt-free month and how soon the first loan is gone. And it asks whether the same money would have done better in savings after tax. A ten-tab workbook you keep (Excel & Google Sheets), plus a guide and an extra-payment log to print.
A one-time purchase you keep and re-run whenever a rate, a balance or a refund changes — no subscription, and no account that stops working when you stop paying.
Planning math, not financial, tax or legal advice. The calculator uses plain monthly amortization and may differ from your lender's figures, especially on loans that accrue interest daily — check your numbers with your lender before you rely on them, and ask them to apply extra payments to principal. The sample loan is fictional and every figure attached to it is invented for illustration. Once filled in, the file holds your own loan details — clear them before you pass a copy on. Free to use; please don't resell or redistribute.