Loan Calculator

How the loan calculator works

This calculator turns four inputs — the amount you borrow, the interest rate, the term, and any extra monthly payment — into your real monthly payment, the total interest you will pay, and a year-by-year amortization schedule. It works for any fixed-rate installment loan: a mortgage, an auto loan, a personal loan, or a student loan. Everything recalculates instantly as you type, and the math runs entirely in your browser — there is no backend crunching your numbers, and we keep no database of what you enter.

The monthly payment comes from the standard amortization formula, which is the same math every lender uses:

Each month, part of your payment covers interest on the balance you still owe, and the rest reduces the balance (the principal). Because interest is charged on the remaining balance, and that balance is highest at the start, your earliest payments are mostly interest. As the balance falls, more of each fixed payment attacks the principal — which is why the amortization schedule below the calculator shows the interest portion shrinking every year.

Interest rate vs. APR: which number to enter

Enter your annual interest rate — the "note rate" on the loan — not the APR. They are not the same thing. The interest rate is what actually determines your monthly payment; the APR (annual percentage rate) is a broader figure that also folds in certain fees, points, and closing costs, so it is usually a little higher. Because this calculator computes principal and interest from the rate alone, using the note rate keeps the payment accurate; typing in the higher APR would overstate what you actually pay each month. If you want to account for fees, add them separately rather than baking them into the rate. For the official distinction, see the CFPB's explainer on the difference between a mortgage interest rate and an APR.

A worked example

How to use the results

• Compare the total interest, not just the monthly payment. A longer term lowers the monthly payment but can dramatically raise the lifetime cost. The "total interest" figure is the honest measure of what a loan costs you.
• Test extra payments before you commit. Even a modest recurring extra payment can shorten the term by years. The calculator shows exactly how much interest and time you save.
• Shop the rate. On a long loan, a rate that is even half a percent lower can save tens of thousands. Run your quote at two different rates and compare the totals.
• Share the exact scenario. Your inputs are stored in the page link, so you can copy it and send your real numbers to a partner or loan officer.

Limitations to keep in mind

This is a clean model of a fixed-rate loan. It does not include property taxes, homeowners or mortgage insurance (PMI), origination fees, or points, all of which affect a real mortgage. It also assumes the rate never changes, so it is not suitable for adjustable-rate loans past their fixed period. Treat the result as an accurate estimate of principal-and-interest, and add the other costs separately. For the exact method, see our methodology page, and for the concept behind the schedule, read how loan amortization actually works.