PayoffTable

Mortgage Extra Payment Calculator

Your mortgage payment includes four things: principal, interest, taxes, and insurance. Only the first two amortize. This calculator works from your actual statement numbers and makes the escrow distinction explicit.

Reviewed by the PayoffTable editorial team · Updated 2026-10-24

Your numbers

Principal remaining from your statement
Your note rate
From your statement
On top of the full P&I payment
Optional — e.g. annual bonus

Runs entirely in your browser. Nothing is uploaded.

Here is the mistake that quietly wastes prepayment money: sending your "extra payment" as a duplicate of the full monthly amount, taxes and insurance included. The servicer applies principal and interest correctly but parks the tax-and-insurance portion as escrow credit — money sitting in their account instead of killing your balance. Extra payments must be principal and interest only.

That is why this calculator starts from your statement's principal balance and note rate, not your monthly payment. The escrow part of your check is a pass-through to your tax collector and insurer; it has zero effect on amortization and belongs nowhere in a payoff calculation.

Enter your balance, rate, and remaining years from your latest statement, add the monthly extra principal you intend to autopay, and the result is your honest new timeline. The number you see is the number that shows up in your mailbox years earlier.

How extra principal works on an existing mortgage

Your scheduled payment is fixed by contract; extra principal rides on top of it, every month, permanently reducing the balance that next month's interest is calculated on. The effect is identical whether your loan is two years old or twenty: interest_m = balance_m × r, and the extra shrinks balance_m for every m that follows.

The calculator simulates this month by month on your real remaining term. It deliberately excludes escrow from both the baseline and the scenario — your tax and insurance obligations do not change when you prepay principal, and mixing them into an amortization model produces wrong payoff dates.

new_balance_m+1 = balance_m − (payment − balance_m × r) − extra_m escrow excluded

One practical note: most servicers let you set an automatic monthly extra in their online portal, designated for principal. Set it once and the habit runs without willpower — the single highest-leverage automation in household finance.

Worked example. Balance $285,000 at 6.25%, 24 years remaining. Baseline: payoff Oct 2050, interest $265,902.37. Add $150/month principal-only: payoff Mar 2047 — 43 months sooner, $46,013.43 interest saved. The $150 costs $36,750.00 over those years — a 125% risk-free, tax-free return on every extra dollar.

Terms & definitions

Amortization
The process of paying off a loan with scheduled payments that cover both interest and principal. Early payments are mostly interest; later payments are mostly principal.
Principal
The amount you borrowed and still owe. Extra payments reduce principal directly, which shrinks every future interest charge.
APR
Annual Percentage Rate — the yearly cost of the loan including fees. Your monthly interest charge uses the note rate, which is usually a touch lower.
Term
The number of years the loan is scheduled to last. A 30-year term has lower payments but roughly double the total interest of a 15-year term at the same rate.

Frequently asked questions

Should my extra payment include taxes and insurance?
No. Extra payments should be principal-and-interest only, labeled "additional principal" in your servicer's portal. If you mail a check that duplicates your full PITI payment, the escrow portion becomes idle credit instead of balance reduction.
Does my escrow payment change when I prepay principal?
Not because of the prepayment. Escrow is recalculated when your taxes or insurance premiums change, and drops off entirely when the loan is paid off. Prepaying principal does not itself trigger an escrow change.
What if my servicer doesn't have an "extra principal" field?
Call the number on your statement and ask how to designate principal-only payments. Every major servicer supports it — it may be behind a "payment options" or "curtailment" menu. For mailed payments, write "apply to principal" on the check and include your loan number.
Does extra principal help more early or late in the loan?
A dollar of principal saves more interest the earlier it lands, because it compounds longer. The same $150/month on a loan with 24 years left saves more than on one with 5 years left. But it helps at every stage — there is no point at which extra principal stops working.

References

  1. CFPB — What is an escrow account?
  2. CFPB — What is an amortization schedule?
  3. Federal Reserve — Mortgage origination resources (APR vs note rate)
Educational content only — not financial, tax, or legal advice. Your loan terms govern; confirm details with your servicer.

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