How It Works
This first derives your standard monthly principal-and-interest payment from your remaining balance, rate, and term using the fixed-rate amortization formula, then simulates the payoff month by month.
If you add an extra monthly payment, the simulation runs a second time with that amount applied entirely to principal, so you can see the exact difference in payoff time and total interest.
Formula
- M — Monthly principal & interest payment
- P — Current remaining balance
- i — Monthly interest rate (annual rate ÷ 12)
- n — Remaining number of monthly payments
Example
Example inputs: $250,000 balance, 6.5% rate, 27 years remaining, $200/mo extra payment.
Result: Current payment: $1,638.89/mo. Paying $200 extra pays it off 77 months sooner and saves $77,121.46 in interest.
Frequently Asked Questions
Where do I find my current balance and remaining term?
Both are on your mortgage servicer's statement or online account — look for 'principal balance' and either the remaining term or your original payoff date.
Does extra principal always go directly to the balance?
With most lenders, yes, if you specify it as an extra principal payment — but confirm with your servicer, since some require you to explicitly mark the extra amount to avoid it being held as a partial future payment.
Is paying off a mortgage early always the best move?
It guarantees a return equal to your mortgage rate on that money, which can be attractive — but it also ties up cash that could go toward other goals, and this calculator doesn't compare that trade-off for you.
This calculator provides estimates for informational purposes only and should not be considered financial, tax, or legal advice.