Estimate your monthly mortgage payments accurately.
$
$
Years
%
$
$
$
Total Monthly Payment$0.00
Principal & Interest:$0.00
Property Tax (Monthly):$0.00
Home Insurance (Monthly):$0.00
HOA Fees:$0.00
Total Interest Paid (Over Term):$0.00
Total Cost of Loan:$0.00
function calculateMortgage() {
// 1. Get input values
var homePrice = parseFloat(document.getElementById("homePrice").value) || 0;
var downPayment = parseFloat(document.getElementById("downPayment").value) || 0;
var loanTermYears = parseFloat(document.getElementById("loanTerm").value) || 0;
var interestRateAnnual = parseFloat(document.getElementById("interestRate").value) || 0;
var propertyTaxAnnual = parseFloat(document.getElementById("propertyTax").value) || 0;
var homeInsuranceAnnual = parseFloat(document.getElementById("homeInsurance").value) || 0;
var hoaFeesMonthly = parseFloat(document.getElementById("hoaFees").value) || 0;
// 2. Validate essential inputs to avoid Infinity/NaN
if (homePrice <= 0 || loanTermYears <= 0) {
// Don't show results if inputs are invalid or incomplete
return;
}
// 3. Perform Calculations
var loanAmount = homePrice – downPayment;
var monthlyInterestRate = (interestRateAnnual / 100) / 12;
var totalPayments = loanTermYears * 12;
// Principal and Interest Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var monthlyPrincipalInterest = 0;
if (interestRateAnnual === 0) {
monthlyPrincipalInterest = loanAmount / totalPayments;
} else {
var x = Math.pow(1 + monthlyInterestRate, totalPayments);
monthlyPrincipalInterest = (loanAmount * x * monthlyInterestRate) / (x – 1);
}
// Monthly Taxes and Insurance
var monthlyTax = propertyTaxAnnual / 12;
var monthlyInsurance = homeInsuranceAnnual / 12;
// Total Monthly Payment
var totalMonthly = monthlyPrincipalInterest + monthlyTax + monthlyInsurance + hoaFeesMonthly;
// Total Loan Metrics
var totalAmountPaid = (monthlyPrincipalInterest * totalPayments);
var totalInterestPaid = totalAmountPaid – loanAmount;
var totalCostOfLoan = totalAmountPaid + downPayment; // Cost of house + interest
// 4. Update UI
document.getElementById("resultsArea").style.display = "block";
// Helper to format currency
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2,
maximumFractionDigits: 2
});
document.getElementById("totalMonthlyPayment").innerText = formatter.format(totalMonthly);
document.getElementById("principalInterest").innerText = formatter.format(monthlyPrincipalInterest);
document.getElementById("monthlyTax").innerText = formatter.format(monthlyTax);
document.getElementById("monthlyInsurance").innerText = formatter.format(monthlyInsurance);
document.getElementById("monthlyHoa").innerText = formatter.format(hoaFeesMonthly);
document.getElementById("totalInterest").innerText = formatter.format(totalInterestPaid);
document.getElementById("totalCost").innerText = formatter.format(totalAmountPaid + (monthlyTax * totalPayments) + (monthlyInsurance * totalPayments) + (hoaFeesMonthly * totalPayments));
// Note: Total Cost displayed includes all taxes/fees over the life of the loan + principal + interest
}
Understanding Your Mortgage Calculation
Calculating your monthly mortgage payment is a critical step in the home-buying process. This Mortgage Payment Calculator helps you estimate your monthly housing costs by factoring in not just the loan repayment, but also necessary additional costs like property taxes, homeowner's insurance, and HOA fees.
How the Mortgage Formula Works
The core of a mortgage payment is the Principal and Interest (P&I). The formula used by lenders to determine this portion is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
M = Total monthly payment
P = Principal loan amount (Home Price minus Down Payment)
i = Monthly interest rate (Annual rate divided by 12)
n = Total number of payments (Loan term in years multiplied by 12)
Key Factors Affecting Your Payment
While the interest rate and loan amount are the biggest drivers, other factors significantly impact your monthly budget:
Down Payment: A larger down payment reduces your principal loan amount, which lowers both your monthly P&I payment and the total interest paid over the life of the loan.
Loan Term: A 30-year term offers lower monthly payments but results in higher total interest costs compared to a 15-year term.
Escrow Costs: Property taxes and home insurance are often bundled into your monthly payment through an escrow account. These costs vary significantly by location and property value.
What is PMI?
If your down payment is less than 20% of the home price, lenders often require Private Mortgage Insurance (PMI). While this calculator includes taxes and insurance, be sure to account for PMI if you are making a smaller down payment. PMI typically costs between 0.5% and 1% of the loan amount annually.
How to Use This Result
Use the "Total Monthly Payment" figure to calculate your Debt-to-Income (DTI) ratio. Most financial advisors recommend that your total housing payment should not exceed 28% of your gross monthly income to ensure financial stability.