Mortgage Payoff Calculator

Estimate how extra payments—monthly or one‑time—can shorten your mortgage term and reduce total interest. Built for homeowners, buyers, and financial pros seeking precise, accessible results fast.

Calculator Inputs

Exclude escrow, fees, and interest due—principal only.
Nominal annual rate; we convert to a monthly rate using r/12.
Enter years and months left on your loan. At least one must be greater than zero.
Extra payment type

Results

Scheduled monthly payment (no extra) $0.00
New payoff time with extra —
Time saved —
Total interest remaining (no extra) $0.00
Total interest with extra $0.00
Interest saved $0.00
Estimated payoff date (with extra) —
Assumes fixed rate, monthly compounding, and on‑time payments. Taxes/insurance/PMI excluded.

Data Source and Methodology

Primary Source: OpenStax, “Business Mathematics,” Section 13.5: Amortized Loans (2018). https://openstax.org/details/books/business-mathematics

Government Guidance: Consumer Financial Protection Bureau (CFPB), “What is amortization and how does it work?” (2020-11-20). https://www.consumerfinance.gov/ask-cfpb/what-is-amortization-en-1065/

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

Monthly rate: i = APR / 100 / 12
Standard payment (given balance B and n months):
M = B · [ i / (1 - (1 + i)^(-n)) ] for i > 0; otherwise M = B / n

New payoff months when adding monthly extra E (no lump sum):
n' = ⎡ - ln(1 - i·B/(M+E)) / ln(1+i) ⎤

Amortization update each month (simulation used for lump sums):
Interest_t = B_t · i ; Principal_t = Payment_t - Interest_t ; B_{t+1} = max(0, B_t - Principal_t)

Glossary of Variables

How It Works: A Step-by-Step Example

Suppose your current balance B = $300,000 at APR = 6% with 25 years remaining (n = 300 months). The monthly rate is i = 0.06/12 = 0.005.

M = 300000 × [ 0.005 / (1 − (1.005)^(-300)) ] ≈ $1,933.28

Now add a monthly extra E = $200, so the total payment is M + E ≈ $2,133.28. Using the payoff formula:

n' = ⎡ − ln(1 − 0.005 × 300000 / 2133.28) / ln(1.005) ⎤ ≈ 255 months

You would be debt‑free about 45 months sooner (3 years and 9 months earlier), saving tens of thousands in interest. If you choose a single lump sum early in the schedule, the calculator simulates amortization month‑by‑month to show the impact precisely.

Frequently Asked Questions (FAQ)

Does the calculator include taxes, insurance, or PMI?

No. It models principal and interest only so you can isolate the effect of extra payments.

What if my APR changes?

This tool assumes a fixed APR. For adjustable‑rate mortgages, results will differ when the rate resets.

Is biweekly payment support available?

Biweekly schedules are not modeled directly, but you can approximate by entering a monthly extra equal to half a payment every month.

Why are my lender’s numbers slightly different?

Lenders may apply daily interest, vary posting dates, and round to the cent each cycle. Those operational details can create small differences.

Can I model multiple lump sums?

This version supports one lump sum. You can approximate multiple by running separate scenarios or using the monthly extra field.

What if my scheduled payment is too low to amortize?

If payment ≤ monthly interest, the balance won’t decrease. Increase the extra payment or verify your remaining term and APR.

How precise are the payoff dates?

Dates are estimated by adding the computed months to today’s date and assume on‑time monthly payments.

Tool developed by Ugo Candido. Content verified by the CalcDomain Editorial Team.
Last reviewed for accuracy on: September 13, 2025.