Mortgage Payoff Calculator
See exactly how much time and interest you'd save by paying extra toward your mortgage principal every month — an exact schedule comparison, not an estimate.
How It's Calculated
Formula
\text{Payment} = B \times \frac{r(1+r)^n}{(1+r)^n - 1}, \quad \text{Extra applied every period: } \text{Reduction}_k = (\text{Payment} - \text{Interest}_k) + \text{Extra}This calculator shows what happens when you add a fixed extra amount to your mortgage payment every month and apply all of it toward principal. Extra principal payments accelerate payoff because they shrink the balance faster than the contractual schedule alone — and since next month's interest is always calculated on a smaller balance, less of every future payment goes to interest and more goes to principal, compounding the effect over the life of the loan. To show this precisely, the calculator builds two complete month-by-month amortization schedules from your current balance, rate, and remaining term: a BASELINE schedule (your current payment, no extra) and an ACCELERATED schedule (your current payment plus the extra amount you enter). Both schedules use the same shared amortization engine, so the time saved and interest saved figures come from comparing two real, fully-computed schedules — not an estimate, a rule of thumb, or a simplified formula. The comparison assumes the same fixed extra amount is paid every month starting immediately, and that your interest rate doesn't change over the remaining term (this tool doesn't model adjustable-rate resets, refinancing, or one-time lump-sum payments — those would need a different model).
Worked Examples
Small balance, meaningful extra payment
- Current balance: $5,000, rate: 12% annual → periodic (monthly) rate = 12% ÷ 12 = 1%
- Remaining term: 5 years → 60 monthly payments, so the current contractual payment ≈ $111.22/month
- Baseline schedule (no extra): pays off in all 60 months, total interest ≈ $1,673.37
- Accelerated schedule (+$200/month): pays off in 18 months instead of 60, total interest ≈ $478.21
- Time saved = 60 − 18 = 42 months (3 years, 6 months). Interest saved = $1,673.37 − $478.21 = $1,195.16
Typical remaining mortgage balance
- Current balance: $300,000, rate: 6% annual, remaining term: 28 years (336 months)
- Baseline schedule (no extra): pays off on the original remaining schedule, at the full contractual total interest
- Accelerated schedule (+$150/month extra): the payoff term shortens and total interest drops, because every extra dollar goes straight to principal and stops accruing interest for every remaining month
- The exact months and dollars saved depend on your specific balance, rate, and remaining term — enter your own numbers above to see your figures
Frequently Asked Questions
Is the interest saved figure an estimate?
No. This calculator builds two complete amortization schedules — one with your extra payment, one without — using the same shared, independently verified amortization engine used across this site's other loan calculators. The interest saved and time saved figures are the exact difference between those two schedules' real totals, not a rule-of-thumb approximation.
What if I enter $0 for the extra payment?
That's a valid input, not an error. With $0 extra, the accelerated schedule is identical to your current (baseline) schedule, so time saved and interest saved both show as zero — this simply confirms what your current schedule already looks like with no acceleration.
Does my lender allow me to pay extra toward principal without restriction?
This calculator assumes every extra dollar you enter goes entirely toward principal every month with no restriction — but that isn't universally true of every mortgage. Some loans carry prepayment penalties or other restrictions on extra principal payments. Check your loan agreement or ask your lender directly before committing to an extra-payment plan; this tool doesn't check your specific loan terms and nothing here is legal or lending advice.
Do I enter my original loan amount or my current balance?
Enter your CURRENT remaining balance — the amount you'd owe if you paid off the mortgage today, from your latest statement. Using the original loan amount instead would overstate both schedules, since it ignores payments you've already made.
What if my interest rate changes later (adjustable-rate mortgage)?
This calculator assumes a fixed rate for the entire remaining term you enter. It doesn't model adjustable-rate resets, refinancing, or rate changes of any kind. If you have an adjustable-rate mortgage, treat these figures as valid only for as long as your current rate holds, and re-run the calculator after any rate change.
Can I model a one-time extra payment instead of a monthly amount?
Not with this calculator — it only models a constant extra amount applied every month starting immediately, not an irregular or one-time lump-sum payment. A single lump-sum payment would need a different calculation model.