Calculating your potential mortgage payment is the first step in the home buying journey. This comprehensive calculator breaks down the "PITI" (Principal, Interest, Taxes, and Insurance) to give you a realistic view of your monthly housing costs. Unlike simple calculators, this tool accounts for Homeowners Association (HOA) fees and Private Mortgage Insurance (PMI), which can significantly affect affordability.
Key Components of the Calculation
Principal & Interest: This is the core of your loan repayment. The amount is determined by the loan amount (Home Price minus Down Payment), the interest rate, and the loan term (usually 15 or 30 years).
Property Taxes: Local governments assess taxes based on your property value. This calculator divides your annual tax estimation by 12 to find the monthly impact.
PMI (Private Mortgage Insurance): If your down payment is less than 20%, lenders typically require PMI. This protects the lender if you default. It is calculated here as a percentage of the original loan amount.
How Interest Rates Affect Buying Power
Even a small change in interest rates can have a large impact on your monthly payment. For example, on a $300,000 loan, a 1% increase in interest rate can raise the monthly payment by over $150. Use the "Interest Rate" field above to test different scenarios to see what fits your budget best.
function calculateMortgage() {
// Get Input Values
var price = parseFloat(document.getElementById('homePrice').value);
var down = parseFloat(document.getElementById('downPayment').value);
var rate = parseFloat(document.getElementById('interestRate').value);
var years = parseInt(document.getElementById('loanTerm').value);
var taxYear = parseFloat(document.getElementById('propertyTax').value);
var insYear = parseFloat(document.getElementById('homeInsurance').value);
var pmiRate = parseFloat(document.getElementById('pmi').value);
var hoaMonth = parseFloat(document.getElementById('hoa').value);
// Validation
if (isNaN(price) || isNaN(down) || isNaN(rate) || isNaN(years)) {
alert("Please enter valid numbers for Price, Down Payment, Rate, and Term.");
return;
}
// Core Calculations
var loanAmount = price – down;
var monthlyRate = (rate / 100) / 12;
var totalPayments = years * 12;
// Principal & Interest Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var monthlyPI = 0;
if (rate === 0) {
monthlyPI = loanAmount / totalPayments;
} else {
monthlyPI = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, totalPayments)) / (Math.pow(1 + monthlyRate, totalPayments) – 1);
}
// Taxes and Insurance
var monthlyTax = taxYear / 12;
var monthlyIns = insYear / 12;
// PMI Calculation
// PMI is typically calculated on the loan amount annually, then divided by 12
// Usually only applies if down payment 80 && pmiRate > 0) {
monthlyPMI = (loanAmount * (pmiRate / 100)) / 12;
} else {
// Even if user entered a rate, if LTV is < 80, PMI is usually 0.
// However, for strict calculator logic based on user input, if they explicitly put a rate,
// we might display it, but standard logic removes it.
// Let's enforce the 20% equity, we set it to 0.
// Just to be safe, if they entered 0, it stays 0.
var totalMonthly = monthlyPI + monthlyTax + monthlyIns + monthlyPMI + hoaMonth;
// Formatting currency
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
});
// Update DOM
document.getElementById('resPI').innerHTML = formatter.format(monthlyPI);
document.getElementById('resTax').innerHTML = formatter.format(monthlyTax);
document.getElementById('resIns').innerHTML = formatter.format(monthlyIns);
document.getElementById('resPMI').innerHTML = formatter.format(monthlyPMI);
document.getElementById('resHOA').innerHTML = formatter.format(hoaMonth);
document.getElementById('resTotal').innerHTML = formatter.format(totalMonthly);
// Show result section
document.getElementById('result').style.display = 'block';
}