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Mortgage / loan calculator: understand the payment and the payoff

A monthly payment is only one part of a borrowing decision. Estimate principal and interest, add the ownership costs you enter, and see whether the loan leaves a balance due at maturity.

Your Expert Online editorial tool · Updated 22 October 2026 · USD · No account needed.

Use the calculator ↓ · Guide and worked example ↓

03 / Understand the payment

Mortgage / loan calculator

Estimate fixed-rate, monthly principal and interest, separate ownership costs, and the remaining balance at maturity. Assumes payments at month-end and monthly interest equal to the annual rate divided by 12.

Amount borrowed, after any down payment.
Fixed nominal rate, not APR; no rate forecast.
360 = 30 years; 180 = 15 years. Must be at least 1.
Set equal to amortization for a fully amortizing loan. A shorter maturity leaves a balance due.
Optional budget item; enter 0 for non-property loans.
Separate from mortgage insurance.
May be paid separately from your lender.
Assumed constant; enter your own estimate or 0.

USD throughout. Hypothetical starting values. Calculations run in your browser; this calculator code does not send or save your inputs.

Method, assumptions and limits

Monthly payment = P × r / (1 − (1 + r)−n), where P is the loan amount, r is the monthly rate and n is the amortization in months. At 0% interest, payment = P ÷ n. Remaining balance is calculated after each scheduled payment through maturity. A balance due at maturity is additional to that month’s regular payment.

Excludes closing costs, fees, points, extra payments, variable rates, interest-only periods and lender-specific rounding or day-count rules. Interest shown is through the entered maturity, not an APR or a lender quote. The monthly budget adds tax, property insurance, HOA and mortgage insurance to principal and interest; it excludes maintenance, utilities and other costs you have not entered.

See the CFPB on payment components and balloon payments. Definitions checked 21 October 2026.

How to use the loan calculator

  1. Enter the amount borrowed. Use the loan principal, not the purchase price. A down payment reduces the amount borrowed; it is not a monthly payment.
  2. Use the fixed interest rate and the payment schedule. Enter the nominal annual rate, not APR. Amortization describes the period used to calculate payments. Maturity is when the loan must be repaid. Enter 360 months for 30 years, 180 for 15 years or 60 for five years.
  3. Separate the extra costs. Enter annual property tax and property insurance, then monthly HOA dues and mortgage insurance. These inputs create a budget total; they do not mean every charge is paid through the lender.
  4. Check the balance due. If maturity is shorter than amortization, plan for the remaining principal in addition to the regular final-month payment.

Worked example: the same loan, two maturity dates

Hypothetical—not a rate quote. Borrow $300,000 at a fixed 6.5% rate, with payments calculated over 360 months. Monthly principal and interest are approximately $1,896.20. Adding $3,600 annual property tax and $1,800 annual insurance brings the entered monthly budget to $2,346.20, before maintenance, utilities or other unentered costs.

With maturity at month 360, the modeled balance is zero after the final payment. If maturity is instead month 60, the monthly principal-and-interest payment stays the same, but approximately $280,832.93 remains due after the 60th regular payment. A lower monthly payment is not evidence that the maturity obligation is manageable.

For a zero-interest check, $120,000 paid over 120 months is $1,000 per month before extras. The calculator handles 0% without dividing by zero.

Questions to ask before relying on the estimate

  • Does the actual loan have a fixed rate, monthly payments and the same amortization and maturity entered here?
  • Are fees, points, prepayment charges or an interest-only period missing from this illustration?
  • Are taxes and insurance already included in another budget, creating a double count?
  • If a balance remains due, what evidence supports the proposed refinance or other repayment plan?

Payment does not establish affordability

This tool does not assess income, credit, reserves or lender approval. Its scheduled interest total excludes fees and uses unrounded payments internally; a lender’s schedule can differ. Compare the result with your actual loan documents.

For investment property, multiply monthly principal and interest by 12 before entering annual debt service in the financing stress test. Include property taxes and insurance in operating expenses there, not in debt service. If work is planned, build a separate renovation budget.