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How do I calculate my monthly mortgage payment?

Short answer

The principal and interest payment comes from the standard amortization formula: M = P x [r(1+r)^n] / [(1+r)^n - 1], where P is the loan amount, r is the monthly interest rate and n is the number of monthly payments. As a worked example only, a 300,000 loan over 30 years at an example rate of 6 percent works out to 1,798.65 per month. Your real payment depends entirely on the rate and term you are offered, and a free mortgage calculator lets you try any combination instantly.

What actually drives the payment

Three inputs set the principal and interest figure: the amount borrowed, the interest rate, and the term. The rate has a bigger effect than most people expect. Using the same example 300,000 loan over 30 years, moving the example rate from 6 percent to 7 percent raises the payment from 1,798.65 to 1,995.91, a difference of 197.26 every month. These rates are illustrations, not quotes; only your lender can tell you your rate.

Principal and interest is not the whole housing payment

The formula covers principal and interest only. Property taxes, homeowners insurance, mortgage insurance if your down payment is small, and any HOA dues get added on top, often through an escrow account. When you budget, calculate the principal and interest figure first, then stack the extras to get the real monthly cost.

Step by step

  1. Enter the loan amount. Type the amount you plan to borrow, not the home price.
  2. Enter your rate and term. Use the rate your lender quoted and the term in years, commonly 15 or 30.
  3. Compare scenarios. Change the rate or term and watch the payment update instantly to compare options.

Frequently asked questions

Does the formula include property taxes and insurance?

No. It produces the principal and interest payment only. Taxes, insurance and any HOA fees are added on top of that figure.

How much difference does one percentage point of rate make?

In the worked example of a 300,000 loan over 30 years, moving from 6 percent to 7 percent raises the monthly payment by 197.26, from 1,798.65 to 1,995.91.

Is a shorter term cheaper?

A shorter term means a higher monthly payment but less total interest over the life of the loan, because you borrow the money for less time.

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