Mortgage Calculator — Principal & Interest

A mortgage payment calculator helps home buyers estimate the cost of a fixed-rate home loan. Use it to calculate a mortgage payment, compare an extra payment, and see how taxes or homeowners insurance can change the monthly estimate.

How to use this mortgage calculator

1. Enter the amount you expect to borrow, not the home’s full purchase price.
2. Add the annual interest rate and repayment term supplied in your loan scenario.
3. Optionally enter an extra monthly principal payment, annual property tax, or annual homeowners insurance.
4. Review monthly principal and interest, estimated PITI when applicable, and the totals.

How the mortgage calculator math works

The monthly mortgage payment calculator converts the annual rate into a monthly decimal rate and the loan term into a number of monthly payments. It then applies the fixed-payment amortization formula:

M = P × r × (1 + r)ⁿ ÷ ((1 + r)ⁿ − 1)

Here, P is the starting principal, r is the annual rate divided by 12 and 100, and n is the number of years multiplied by 12. Property tax and insurance are divided by 12 and added only when you provide them. An extra payment is applied to principal, which can shorten the modeled payoff period and reduce interest.

Worked example

Consider an example $300,000 fixed-rate loan with a 6.5% annual interest rate and a 30-year term. The monthly rate is 0.065 ÷ 12, and the term contains 360 payments. Substituting those values into the formula produces a monthly principal-and-interest estimate of $1,896.20. Taxes, insurance, HOA charges, mortgage insurance, and lender fees are not part of that figure unless entered separately where the calculator provides a field.

Use the mortgage payment calculator again with a different loan amount, term, or extra payment to compare scenarios. A mortgage payment calculator is most useful when each input comes from the same written loan estimate or a lender-provided scenario.

Assumptions and limits

• The calculation models a fully amortizing, fixed-rate loan with monthly payments.
• Rates and lender terms can change. Every rate entered here is an example that you should verify with your lender.
• The mortgage monthly payment calculator excludes PMI, HOA dues, closing costs, escrow adjustments, and special assessments.
• Taxes and insurance come from your entries and may differ from actual bills.
• Results are rounded for display and are educational estimates, not underwriting decisions.

Mortgage calculator FAQ

Does the monthly result include property taxes?

Only when you enter an annual property-tax amount. The tool divides that entry by 12 and includes it in the PITI estimate.

What happens when I add an extra monthly payment?

The extra amount is applied to principal in the model. That generally reduces the number of payments and projected interest, but confirm that your servicer applies additional funds to principal and does not charge a prepayment fee.

Why might my lender’s payment be different?

A lender may use different rounding, payment timing, escrow estimates, mortgage insurance, or loan-specific charges. Review your Loan Estimate and closing documents for the authoritative figures.

Related mortgage planning resources

Browse the Zarvis calculators collection as additional mortgage tools are reviewed and approved. If you are deciding whether to keep cash available or make a larger payment, the high-yield savings account guide explains liquidity and savings considerations. The Consumer Financial Protection Bureau’s loan-options guide provides information about comparing mortgage structures.

Last reviewed: October 5, 2026
Author: Harsh Kardam

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Disclaimer: This is an educational estimate, not a rate quote, approval, or financial, legal, or tax advice. Verify current rates, fees, and terms directly with your lender or provider.