Extra Mortgage Payment Calculator
Extra payment savings and payoff time
How Much Does an Extra Mortgage Payment Save?
This calculator uses your current loan balance, interest rate, and time left on the loan to compute your scheduled principal-and-interest payment, then compares paying only that amount to paying extra toward principal. Extra payments reduce future interest because the balance drops faster. One-time prepayment is modeled as a lump applied to principal now while your payment stays the same (shortening the loan). Monthly extra is the same dollar amount every month. Annual extra is one lump at the end of each 12-month period. Actual servicer rules, rounding, and escrow can differ slightly. Use the Extra Mortgage Payment Calculator to get a clear result you can act on right away.
Schedule uses 300 months (25.00 years).
Monthly extra is added to principal each month on top of the normal principal portion.
Scheduled P&I (level payment)
$2,161
Baseline total interest (no extra)
$328,199
Interest saved vs baseline
$69,082
Total interest with extra
$259,117
Payoff with extra
20 yr 6 mo
Baseline was 25 yr
Time cut from loan
4 yr 6 mo
Remaining balance over time
Original amortization vs your balance with the extra payment plan (month 0 = now).
The Formula
How to Calculate Manually
- 1
Enter your current mortgage balance (not the original loan amount unless they match).
- 2
Enter the annual interest rate on your loan.
- 3
Enter how much time is left - either as years or total months.
- 4
Choose whether your extra paydown is one-time, every month, or once per year.
- 5
Enter the extra amount and read payoff time, interest saved vs no extra payments.
Examples
$320,000 balance, 6.5% rate, 25 years left - what does $200/month extra do vs paying only the scheduled payment?
With no extra payment, total interest over the remaining term is on the order of $328,000. Adding $200 to principal every month cuts that by roughly $69,000 and pays off the loan about 4.5 years sooner, because each month your balance is lower so less interest accrues the next month. A one-time payment of the same total dollars does not do the same thing: only recurring extra keeps reducing the balance month after month.
$400,000 balance, 6.5%, 30 years left - one-time $10,000 toward principal vs putting $0 extra.
With no extra, total interest is on the order of $510,000 over the full amortization. A single $10,000 lump (modeled as applied now, same contractual payment afterward) drops total interest by roughly $55,000 and shortens the loan by about two years. The tradeoff vs recurring extra: the lump helps once, but it does not repeat - there is no additional principal next month unless you pay extra again.
Same extra dollars per year: $200 every month vs $2,400 once per year - why are they different?
Roughly the same cash per year ($200 × 12 ≈ one $2,400 annual payment), but monthly extra wins a bit more interest savings because principal drops earlier in the year, so you pay less interest every month in between. The calculator shows a few thousand dollars more saved with steady monthly extra than with one annual lump of the same annual total. Use "Every month" vs "Once per year" with matching totals to compare on your own loan.
💡 Tips
- •Confirm your actual scheduled payment with your lender if you want to match the statement exactly.
- •Biweekly plans and rounding behave differently; use "monthly" for a steady extra amount each month.
- •Build an emergency fund before large prepayments; prepaid principal is illiquid until you sell or refinance.
🎉 Fun Facts
- •Early payments are mostly interest: extra principal in the first few years often saves more total interest than the same dollars later.
- •Matching "one extra payment per year" is close to adding roughly 1/12 of your payment every month.
- •A lower balance today means less interest accrues next month - that is why prepayment accelerates payoff.