Estimate your monthly mortgage payments accurately.
Understanding Your Mortgage Calculation
A mortgage calculator is an essential tool for prospective homebuyers to determine affordability. While the listing price of a home is a fixed number, your actual monthly obligation is composed of several dynamic factors. This calculator helps you visualize how interest rates, down payments, and loan terms impact your monthly budget.
Key Components of Your Monthly Payment
Your total monthly mortgage payment (PITI) typically consists of four main parts:
Principal: The portion of the payment that goes toward paying down the loan balance.
Interest: The cost of borrowing money, paid to the lender. In the early years of a mortgage, a significant portion of your payment goes toward interest.
Taxes: Property taxes assessed by your local government, often held in escrow by your lender.
Insurance: Homeowners insurance to protect against hazards, plus private mortgage insurance (PMI) if your down payment is less than 20%.
How Interest Rates Affect Affordability
Even a small fluctuation in interest rates can drastically change your buying power. For example, on a $400,000 loan, a 1% increase in interest rate can add hundreds of dollars to your monthly payment and tens of thousands of dollars to the total cost of the loan over 30 years.
Tips for Lowering Your Mortgage Payment
If the calculated monthly payment is higher than your budget allows, consider these strategies:
Increase your down payment to reduce the principal loan amount.
Improve your credit score to qualify for a lower interest rate.
Shop around for cheaper homeowners insurance policies.
Look for homes in areas with lower property tax rates.
function calculateMortgage() {
// 1. Get Input Values
var price = parseFloat(document.getElementById('homePrice').value);
var down = parseFloat(document.getElementById('downPayment').value);
var termYears = parseFloat(document.getElementById('loanTerm').value);
var rateAnnual = parseFloat(document.getElementById('interestRate').value);
var taxAnnual = parseFloat(document.getElementById('propertyTax').value);
var insuranceAnnual = parseFloat(document.getElementById('homeInsurance').value);
var hoaMonthly = parseFloat(document.getElementById('hoaFees').value);
// 2. Validate Inputs
if (isNaN(price) || price < 0) price = 0;
if (isNaN(down) || down < 0) down = 0;
if (isNaN(termYears) || termYears <= 0) termYears = 30; // default to 30 if invalid
if (isNaN(rateAnnual) || rateAnnual < 0) rateAnnual = 0;
if (isNaN(taxAnnual) || taxAnnual < 0) taxAnnual = 0;
if (isNaN(insuranceAnnual) || insuranceAnnual < 0) insuranceAnnual = 0;
if (isNaN(hoaMonthly) || hoaMonthly < 0) hoaMonthly = 0;
// 3. Calculation Logic
var loanAmount = price – down;
var numPayments = termYears * 12;
var monthlyRate = (rateAnnual / 100) / 12;
var monthlyPI = 0; // Principal and Interest
if (loanAmount <= 0) {
monthlyPI = 0;
} else if (rateAnnual === 0) {
monthlyPI = loanAmount / numPayments;
} else {
// Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var mathPower = Math.pow(1 + monthlyRate, numPayments);
monthlyPI = loanAmount * (monthlyRate * mathPower) / (mathPower – 1);
}
var monthlyTax = taxAnnual / 12;
var monthlyInsurance = insuranceAnnual / 12;
var totalMonthlyPayment = monthlyPI + monthlyTax + monthlyInsurance + hoaMonthly;
// 4. Formatting Function
function formatCurrency(num) {
return '$' + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
// 5. Build Result HTML
var resultHTML = '';
resultHTML += '