Mortgage Payoff Accelerator Calculator

This calculator runs the same month-by-month mortgage simulation twice — once at the standard payment only, once adding Extra Monthly Payment and any Extra Annual Payment (lines 3-28) — and reports the gap between the two runs. The standard payment itself is solved with the classic amortization formula (lines 92-100) to be exactly the amount that clears Mortgage Balance in Original Loan Term years, so unlike Extra Payment Impact's sibling calculator, there's no interest-floor check here — a fully amortizing standard payment always covers its own interest by construction. Original Loan Term dominates both headline outputs: a 10% nudge moves Time Saved by roughly 38% and Interest Saved by roughly 43%, ahead of Mortgage Balance (about 14% and 8%) and Interest Rate (about 5% and 31%) — because shortening the original term raises the standard payment itself before any extra payment is even added, compounding with whatever extra you contribute. Loan Balance instead dominates Accelerated Total Interest specifically (about 27%, ahead of Interest Rate's roughly 21%), since a bigger starting balance means more principal accrues interest throughout the accelerated schedule even after extra payments are applied.

Extra Monthly Payment and Extra Annual Payment never move Standard Total Interest at all, because that figure comes from the standard-only simulation, which by definition never sees either extra payment. Extra Annual Payment moves every output by only a few dollars at these defaults — a once-a-year lump sum simply has far less compounding leverage than a payment applied every month. This calculator does not model refinancing, changing rates, or PMI removal thresholds.