About & Methodology

What this site is

Mortgage Payoff Calculator is a small collection of free, fast mortgage tools built to answer one practical question: when will my mortgage actually be paid off, and how can I get there sooner? There is nothing to install and no account to create. You enter a few numbers and get an instant, transparent estimate. The site includes three calculators:

• Mortgage Payoff Calculator — enter your balance, interest rate, and monthly payment to see how long until you are debt-free, your payoff date, and total interest, plus the savings from an optional extra payment.
• Mortgage Recast Calculator — see your new, lower monthly payment after a lump-sum principal payment is re-amortized over the same remaining term, and the interest you would save.
• Mortgage Calculator With Extra Payments — see how an extra monthly amount, a one-time lump sum, or both shorten your loan and cut total interest.

How the math works

Every result on this site comes from a standard amortization calculation — the same method lenders use to build a repayment schedule. We do not use shortcuts or rules of thumb; we simulate your loan one month at a time.

Monthly interest

Interest is compounded monthly. We convert your annual interest rate (APR) into a monthly periodic rate by dividing by 12. For example, a 6.5% APR becomes a monthly rate of 6.5% ÷ 12 ≈ 0.5417% per month. Each month, interest is charged on the remaining balance, so as the balance falls, the interest portion of each payment falls with it.

The monthly payment

Where a calculator needs to derive the standard principal-and-interest payment from a balance, rate, and term, it uses the standard fixed-rate mortgage payment formula:

M = P × r × (1 + r)ⁿ÷ ((1 + r)ⁿ− 1)

where M is the monthly payment, P is the loan principal, r is the monthly interest rate, and n is the number of monthly payments in the term. (If the rate is zero, the payment is simply the balance divided by the number of months.)

Building the schedule

We then step through the loan month by month. For each month we:

1. Calculate that month’s interest as the remaining balance multiplied by the monthly rate.
2. Subtract the interest from your payment (including any extra amount or one-time lump sum) to find how much principal is repaid.
3. Reduce the balance by that principal, and add the interest to a running total.

The final payment is automatically trimmed so the balance lands exactly on zero rather than going negative.

How each headline figure is derived

• Time to pay off & payoff date. We count the number of months it takes for the balance to reach zero. Your payoff date is simply today’s date plus that number of months.
• Total interest. This is the sum of every month’s interest charge across the full schedule.
• Interest and time saved. For extra payments and recasts, we run two schedules side by side — one at your normal payment and one with the extra amount or lump sum applied — and report the difference in months and in total interest.

Because the calculation is fully deterministic, the same inputs always produce the same result. One safeguard worth noting: if a payment is smaller than the first month’s interest, the balance can never fall, so the tool tells you the loan would not pay off rather than showing a misleading number.

Accuracy and limitations

These tools are designed to be accurate for the inputs you provide, but they are estimates, not a quote or a statement. A few things to keep in mind:

• Principal and interest only. The calculators model your principal-and-interest (P&I) payment. They do not include property taxes, homeowners or hazard insurance, private mortgage insurance (PMI), HOA dues, or escrow. Enter your P&I amount only — not your full monthly housing payment — for an accurate payoff date.
• Fixed-rate assumption. The math assumes a fixed interest rate for the life of the loan. If you have an adjustable-rate mortgage, results will drift as your rate changes.
• Servicer differences. Lenders may round differently, apply payments on different dates, or handle extra principal in their own way. Small differences from your statement are normal.
• Prepayment penalties. Some loans charge a fee for paying ahead. The calculators do not account for prepayment penalties — check your loan documents before making large extra payments.

Why it’s free

We believe a clear answer to “when will my mortgage be paid off?” should not sit behind a paywall. To keep the calculators free for everyone, the site is supported by advertising. Ads let us cover hosting and development costs without charging you. You can read how advertising cookies and your data are handled in our Privacy Policy.