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Mortgage amortization calculator

Enter either your scheduled monthly principal-and-interest payment or your remaining term, then move seamlessly between them. See how each payment divides between principal and interest, with or without extra principal.

By the SterlingCat editorial team · Last updated 2026-08-02 · Uses the verified shared amortization engine (how we calculate)

What this calculator shows

  • The scheduled monthly principal-and-interest payment—not the full escrow payment.
  • Annual principal-versus-interest charts, the remaining principal balance, and exact annual or monthly totals.
  • How explicit extra principal changes payoff time and interest, without deciding whether prepaying is your best use of the money.

Your mortgage

Enter the current terms

$
%

Payment and remaining term

Edit either value; the other updates automatically.

Remaining term
$

Calculated from the remaining term.

Extra principal scenarios (optional)
$

Applied before month 1.

$ a month

Illustrative starting values—not a current rate quote. Principal and interest only; escrow and mortgage insurance are excluded.

Your result

Scheduled monthly principal and interest

—

Total principal
—
Total interest
—
Total paid
—
Payoff time
—

Principal versus interest

Principal
——
Interest
——

This is a mathematical fixed-rate schedule, not a lender statement. Check your agreement for payment allocation, rounding, and prepayment terms.

Explore the amortization

Annual overview

How the mortgage changes over time

Charts and annual totals summarize the selected scenario. Open the payment schedule when you need exact payment-by-payment amounts.

Remaining principal balance
Remaining principal balance by payment year
Principal and interest paid each year
Principal and interest paid by payment year
View annual totals

Each payment year is a consecutive group of up to 12 scheduled payments.

Annual mortgage amortization summary
Payment year Paid Principal Interest Extra principal Ending balance
Totals — — — — $0.00
View the payment schedule

Each payment covers interest first; the rest reduces principal.

Monthly mortgage amortization schedule
Payment Paid Principal Interest Extra principal Balance
Totals — — — — $0.00

A separate decision

Should monthly extra money go here or be invested?

Prepay vs. Invest compares that allocation choice. The handoff carries this balance, rate, remaining term, and monthly extra. A one-time extra is not carried because the comparison models recurring monthly cash.

Add an extra monthly principal amount above to carry this scenario into the comparison.

Calculated in your browser. A copied link stores these numbers in the URL fragment.

How the mortgage calculation works

This is a fixed-rate, level-payment, fully amortizing principal-and-interest schedule. Entering the remaining term derives the scheduled payment; entering the scheduled payment derives the number of payments remaining. At a 0% rate, principal is divided evenly across the term.

Each month, interest equals the opening balance multiplied by the nominal annual rate divided by 12. The scheduled payment covers interest first; the rest reduces principal. A one-time extra is applied before month 1, while a recurring extra is applied after each scheduled payment. Neither extra recasts the scheduled principal-and-interest payment in this model.

Principal and interest—not the full housing payment

Property tax, homeowners insurance, mortgage insurance, homeowners association dues, escrow adjustments, lender fees, and other housing costs are excluded. Use your lender statement when you need the amount actually drafted each month.

Interest rate, not APR

The input is an annual interest rate. It is not labeled annual percentage rate (APR), because this calculator does not include points, origination charges, or other finance charges that may be part of a disclosed APR.

Extra-payment timing

The one-time amount is assumed to reduce principal immediately before the next monthly interest calculation. Recurring extra principal is applied after the scheduled payment every month. A servicer may use different timing, rounding, or allocation rules; confirm that extra payments will be applied to principal and check for any prepayment restrictions.

Internal precision and displayed amounts

Calculations retain full numeric precision through payoff and round only for display. The final payment is capped at the amount still due. Displayed rows can differ by a cent from a lender using a different contractual rounding policy, while the full-precision schedule still reconciles principal, interest, total paid, and a zero ending balance.

Sources

Grounded in authoritative primary sources:

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