40-year Mortgage Calculator

Reviewed by: David Chen, CFA | Real Estate Finance Expert
Last Updated: October 2025

Explore the long-term impact of an extended loan term with our 40-year mortgage calculator. While not a standard offering for most new purchases, 40-year terms are increasingly common in loan modifications and specialized lending programs to maximize monthly cash flow.

40-year mortgage calculator

The principal amount to be financed.
Annual fixed interest rate.
Defaults to 40 years (480 months).
Leave empty to calculate payment.
Estimated Monthly Payment
$0.00
Principal & Interest (40-Year Term)

40-year mortgage calculator Formula

The calculation follows the standard amortization logic but extends the timeline to 480 months, significantly altering the interest-to-principal ratio in the early years.

M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
Source: Investopedia (40-Year Mortgage Explained)

Variables

  • M: Monthly Principal & Interest Payment.
  • P: Principal Loan Amount.
  • i: Monthly interest rate (Annual Rate / 12).
  • n: Total number of payments (40 Years x 12 = 480).

Related Calculators

What is a 40-year mortgage calculator?

A 40-year mortgage calculator is a specialized tool for evaluating loans with an extended amortization period. While not as common as the 30-year fixed mortgage, 40-year terms are often used in high-cost areas for Jumbo loans or as part of loan modification programs to help struggling homeowners reduce their monthly obligations.

By spreading the principal repayment over an additional 10 years, the monthly payment decreases. However, this comes at the cost of paying significantly more interest over the life of the loan.

How to Calculate a 40-Year Mortgage (Example)

  1. Input Loan Amount: Enter the amount borrowed (e.g., $500,000).
  2. Select Rate: Enter the interest rate. Note that 40-year loans often carry slightly higher rates than 30-year loans due to lender risk.
  3. Confirm Term: Ensure 40 years (480 months) is selected.
  4. Analyze: The calculator determines the payment needed to pay off the loan by the end of the 40th year.

Frequently Asked Questions (FAQ)

Is a 40-year mortgage a good idea?

It improves monthly cash flow by lowering payments, making expensive homes more affordable month-to-month. However, it builds equity very slowly and results in massive total interest costs compared to a 30-year loan.

How much lower is the payment on a 40-year mortgage?

Typically, extending the term from 30 to 40 years lowers the monthly principal and interest payment by about 5% to 10%, depending on the interest rate.

Are 40-year mortgages available for new purchases?

They are rare for standard conventional loans but may be available through Non-QM (Non-Qualified Mortgage) lenders or for Jumbo loans.

Does this include taxes and insurance?

No, this calculator provides the Principal and Interest (P&I) figure. You must add property taxes and insurance to see your full housing expense.

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