Mortgage Payoff Calculator
Enter your balance, interest rate, remaining term, and an extra monthly payment to see how much sooner you could be mortgage-free and how much interest you would save.
Model extra payments
Remaining loan balance, from $1 through $100,000,000.
Annual interest rate, from 0% through 25%.
Whole months left on the loan, from 1 through 600 (360 = 30 years).
Added to each monthly payment, from $0 through $1,000,000.
You could save $91,173.44 in interest and pay off 81 months sooner.
- Monthly payment
- $1,798.65
- New payoff time
- 23 years, 3 months
- Months saved
- 81
| Plan | Time to pay off | Total interest |
|---|---|---|
| Without extra | 30 years | $347,514.57 |
| With extra | 23 years, 3 months | $256,341.13 |
Paying extra clears the balance 81 months sooner than sticking with the scheduled payment alone.
How mortgage payoff is calculated
The scheduled monthly payment is the level payment that amortizes your balance over the remaining term at the given rate. The calculator then amortizes the loan twice — once with the scheduled payment and once with your extra amount added each month — and compares the number of months and total interest. Every extra dollar reduces principal directly, so it saves all the future interest that principal would have accrued.
Payment = B × r × (1 + r)n / ((1 + r)n − 1)Each month: interest = balance × r, principal = payment + extra − interest- B
- Remaining loan balance
- r
- Monthly periodic rate (annual rate ÷ 12)
- n
- Remaining term in months
- extra
- Additional principal paid each month
$300,000 at 6% over 360 months, plus $200 extra
A $300,000 balance at 6% over a 360-month term has a scheduled payment of $1,798.65. Left alone, it runs the full 360 months. Adding $200 to every payment pays the loan off in 279 months — 81 months sooner — and saves $91,173.44 in interest.
This is an educational calculation based only on the values you provide. It does not look up your live loan terms, and it is not financial advice.
What this calculator assumes
- The interest rate stays fixed for the whole payoff period.
- The extra payment is applied to principal every month without interruption.
- Taxes, insurance, HOA dues, and PMI are excluded — this models principal and interest only.
- No prepayment penalties or fees are modeled.
- Money values are rounded to the nearest cent for display.
Mortgage payoff FAQ
Why do small extra payments save so much?
Extra payments go entirely toward principal, so they eliminate every future interest charge that principal would have generated. Early in a long, high-balance loan that compounding effect is large, which is why even a modest monthly addition can cut years off the term.
Should I tell my lender the extra is for principal?
Yes. Many servicers apply unspecified extra amounts to the next scheduled payment rather than to principal. Confirm the extra is applied to principal so it reduces the balance the way this model assumes.
Sources and review notes
Methodology last checked Jul 14, 2026. Formula implementation is covered by deterministic unit tests. No financial professional review is claimed yet.