Principal and interest
The calculator models a fully amortizing fixed-rate mortgage. For a loan principal P, monthly interest rate r, and total number of monthly payments n, the scheduled monthly principal-and-interest payment is:
When the annual interest rate is zero, the calculator divides principal by the number of payments.
Total monthly housing estimate
The displayed first-month total adds the scheduled principal-and-interest payment to:
- Property taxes: home price × annual tax rate ÷ 12
- Homeowners insurance: user-entered annual premium ÷ 12
- Estimated PMI: loan amount × user-entered annual PMI rate ÷ 12, when the down payment is below 20%
- Monthly HOA dues entered by the user
These items may be escrowed, billed separately, or change after closing. Special assessments, flood insurance, supplemental insurance, maintenance, utilities, closing costs, points, lender fees, and many loan-specific charges are not included unless expressly entered.
PMI modeling
For a simplified conventional-loan estimate, PMI is displayed when the down payment is below 20%. In the amortization model, estimated PMI stops when the projected balance reaches 80% of the original home price. This is not a determination of actual eligibility to cancel or terminate mortgage insurance. Loan type, appraisal, payment history, seasoning, servicer rules, and law can affect the result.
Extra payments
The extra-payment scenario applies the entered monthly amount directly to principal after the scheduled principal-and-interest payment. Estimated interest savings equal base-schedule interest minus accelerated-schedule interest. Taxes, insurance, HOA dues, and PMI are excluded from the interest-savings calculation because they do not pay down principal.
Affordability ratios
The budget check divides the calculated total monthly housing estimate by gross monthly household income. It also adds user-entered recurring debt payments to display a total debt-to-income ratio. The on-page wording references common planning benchmarks only; it does not predict underwriting or approval.
Official consumer-information sources
- CFPB: How mortgage lenders calculate monthly payments
- CFPB: Principal and interest versus total monthly payment
- CFPB: What is PITI?
- CFPB: What is private mortgage insurance?
- CFPB: Loan Estimate explainer
- CFPB: Figure out how much you want to spend
External sources are provided for consumer education. Their inclusion does not imply endorsement of this website.
Privacy and calculation environment
The calculator JavaScript runs locally in the visitor’s browser. The forms do not send entered home prices, income, debts, rates, or other calculation values to the site owner. Standard server logs or privacy-respecting analytics, if later enabled by the owner, should be disclosed in the privacy policy before deployment.
Review date
Methodology reviewed August 6, 2026. Review the calculator against current law, program guidance, and browser behavior before making material financial decisions.