Mortgage Payment Calculator

Before you calculate

Use this calculator when you want to compare a simple mortgage principal-and-interest estimate before adding property tax, homeowners insurance, mortgage insurance, HOA dues, escrow, closing costs, points, APR, lender underwriting, or product terms. Use Amortization for a month-by-month schedule, House Affordability when income and debt ratios matter, Down Payment when cash-to-close assumptions matter, and lender disclosures for real Loan Estimate or Closing Disclosure figures.

Formula summary

The app calculates loan amount as max(homePrice - downPayment, 0). It converts Annual rate to a monthly decimal rate with annualRate / 100 / 12 and converts Term in years to months with termYears * 12. If the monthly rate is 0, Monthly principal and interest equals loanAmount / months. Otherwise it uses PMT = P * m / (1 - (1 + m)^-n), where P is loan amount, m is monthly rate, and n is total months. Total principal and interest paid equals the full-precision monthly payment times total months, and Total interest equals that total minus loan amount.

Worked example

Example: $400,000 home, $80,000 down, 6.5 percent for 30 years

With the default inputs, a $400,000 home price and $80,000 down payment produce a $320,000 loan amount. At a 6.5 percent annual rate over 30 years, the calculator uses 360 monthly payments and reports $2,022.62 monthly principal and interest, $728,142.36 total principal and interest paid, and $408,142.36 total interest. In the zero-rate fixture, a $300,000 home with $50,000 down, 0 percent rate, and 15-year term divides the $250,000 loan amount into 180 payments of $1,388.89 with $0.00 interest. If the default loan amount and rate use a 15-year term instead, the payment rises to $2,787.54 and total interest falls to $181,757.84.

The example shows how down payment, rate, and term affect the fixed principal-and-interest estimate. It does not include escrow, tax, insurance, mortgage insurance, closing costs, APR, approval, underwriting, or personal borrowing advice.

Assumptions

• The home price, down payment, annual rate, and term stay fixed. The calculator models a level monthly principal-and-interest payment and does not model adjustable rates, interest-only periods, balloon payments, prepayment, late fees, refinancing, escrow changes, property taxes, homeowners insurance, mortgage insurance, HOA dues, closing costs, points, lender credits, or cash-to-close amounts.
• The annual rate input is a user-entered note-rate assumption divided by 12 for the payment formula. It is not automatically a lender APR, Loan Estimate, Closing Disclosure, rate lock, quote, approval, or underwriting result.
• Package fixtures cover the default fixed-rate case and a zero-rate branch, and internal independent comparator checks may be used only as validation evidence. CFPB mortgage payment materials are needed before copy explains principal-and-interest versus total monthly payment boundaries; CFPB Loan Estimate and Closing Disclosure materials are needed before copy discusses lender estimates, projected payments, closing costs, or cash to close; Regulation Z sections 1026.18 and 1026.22 are needed before legal payment-schedule, total-of-payments, finance-charge, APR, or disclosure claims. Results are educational estimates, not financial, tax, legal, lending, mortgage, consumer-rights, regulatory, or personalised advice.

Common mistakes to avoid

• Reading principal and interest as the whole monthly housing payment. Real mortgage bills may also include escrowed taxes, homeowners insurance, mortgage insurance, HOA dues, or other charges.
• Treating the entered annual rate as APR or a lender quote. APR and disclosure figures can include finance charges and timing rules that this calculator does not model.
• Using the result as an affordability decision, approval estimate, tax answer, insurance estimate, closing-cost figure, or product recommendation. Those depend on income, debts, local rules, property details, lender terms, and personal circumstances.

Methodology and sources

This calculator is an original implementation based on documented formulas, app-specific assumptions, deterministic fixtures, edge cases, rounding policy tests, and internal validation. It is not copied from a single source.

Outputs are checked with deterministic fixtures, edge cases, rounding policy tests, and internal independent comparator checks where overlapping outputs are available. The result remains an educational estimate, not a quote, approval, tax answer, or personalised advice.

Formula version 2026.05.20. The version marks the calculation logic and validation fixture set used for this estimate.

• CFPB mortgage payment materials should be used when copy explains principal and interest, taxes, homeowners insurance, mortgage insurance, escrow, or total monthly mortgage-payment boundaries.
• CFPB Loan Estimate and Closing Disclosure materials should be used before copy discusses projected payments, closing costs, cash to close, lender estimates, or final mortgage disclosure figures.
• CFPB APR guidance and Regulation Z sections 1026.18 and 1026.22 should be used before copy discusses APR, payment schedules, total of payments, finance charges, legal disclosures, or Truth in Lending terminology.
• Lender disclosures, servicer documents, local tax authorities, insurers, HOA or co-op documents, legal sources, and relevant local regulators should be used before copy makes product-specific, jurisdiction-specific, approval, underwriting, rate-lock, escrow, tax, insurance, mortgage-insurance, HOA, legal, or consumer-credit claims.

Estimate only

The result is educational and is not financial, tax, legal, lending, investment, or regulated advice. Real provider terms, fees, rates, taxes, and personal circumstances can change the final answer.

Formula and help: read the full mortgage payment calculator methodology notes.

Related reading

• Mortgage payments in plain English
• How Calcs.finance validates calculator formulas
• Estimate limitations and not-advice disclaimer

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