What This Tool Does
Use the calculator to compare your scheduled mortgage payments with a plan that adds a fixed extra payment each month. It uses your remaining balance, annual interest rate, current monthly principal-and-interest payment, optional extra payment, and optional start date. The result reports payoff dates, total interest, interest saved, time saved, and months to payoff.
How to Use the Mortgage Payoff Calculator
- Enter the Remaining mortgage balance ($), Annual interest rate (%), and Current monthly payment ($). Use the principal-and-interest payment, excluding taxes, insurance, and escrow.
- Optionally enter an Extra monthly payment ($, optional). The calculator applies this fixed amount entirely to principal.
- Optionally enter a Start date (optional). Leave it blank to use today's date.
- Click Calculate to show the comparison.
- Click Reset to clear the entered fields and errors and hide the result.
How the Payoff Calculation Works
The calculator converts the annual rate to a monthly rate with Annual rate / 100 / 12. Each simulated month calculates interest, subtracts it from the payment to determine principal, and reduces the remaining balance. It runs this process once with the current payment and again with the current payment plus the extra payment.
Payoff is treated as reached when the remaining balance is at most $0.005. The payoff date is the start date plus the simulated number of months. Interest saved is scheduled-plan interest minus extra-payment-plan interest.
Assumptions and Limitations
- The annual rate and monthly payment stay fixed, with monthly compounding.
- The calculation covers principal and interest only. It excludes property taxes, homeowners insurance, PMI, escrow, fees, refinancing, missed payments, and rate or payment changes.
- Any extra monthly payment is applied entirely to principal.
- The monthly payment must be greater than the first month's interest. Otherwise, the calculator shows an error because the balance would not shrink.
- The scheduled-payment simulation stops with an error if the balance is not paid off within
1,200months, or 100 years.
Read, Copy, or Download the Result
The result shows each payoff date as a month and year, plus interest saved, time saved, and months to payoff with the extra payment. It also displays the formula's intermediate values and a scheduled-versus-extra comparison table.
Use Copy result to place a plain-text summary on the clipboard. Use Download result (.txt) to save the same summary as a text file.
Calculator Inputs and Privacy Scope
Calculations run locally in your browser using the values you enter. The calculator does not fetch live rates, lender records, credit data, or account data, and no lender or account connection is part of its workflow. This describes calculator input processing only; other page features may use their own services.
Frequently Asked Questions
How is the mortgage payoff date calculated?
Starting from your remaining balance, each month's interest is Balance x (Annual rate / 100 / 12), and the rest of the payment reduces the balance. The calculator counts the months until the remaining balance is at most $0.005 and adds those months to your start date.
How is the interest savings from an extra payment calculated?
The calculator runs the payoff simulation twice - once with only your current monthly payment, and once with the current payment plus your extra amount - then subtracts the total interest paid in the extra-payment scenario from the total interest paid in the scheduled-only scenario.
What happens if my monthly payment doesn't cover the interest?
If your entered monthly payment is less than or equal to the first month's interest charge, the balance would never shrink, so the calculator shows a validation error instead of a result.
Does this tool use my actual lender or account data?
No. It only uses the balance, rate, payment, and extra payment you type in. It does not fetch live interest rates, credit records, or any lender or account data, and it is not personalized financial advice.
Does this calculator include taxes, insurance, or escrow?
No. It calculates principal and interest only, applying any extra payment entirely to principal. It does not model property taxes, homeowners insurance, PMI, escrow, fees, or rate changes.