Calculating your monthly mortgage payment is a critical first step in the home buying process. This Mortgage Payment Calculator provides a comprehensive breakdown of your estimated expenses, helping you determine exactly how much house you can afford. Unlike simple calculators, this tool accounts for the "PITI" components: Principal, Interest, Taxes, and Insurance.
Breakdown of Costs
Your monthly payment is typically composed of four main parts:
Principal: The portion of your payment that goes directly toward reducing your loan balance. In the early years of a mortgage, this amount is small but grows over time.
Interest: The cost of borrowing money from your lender. Higher interest rates significantly increase your monthly payment and the total cost of the loan.
Property Taxes: Taxes paid to your local government, usually collected by the lender in an escrow account and paid annually on your behalf.
Homeowners Insurance: Protects your property against damage. Like taxes, this is often divided into monthly payments and held in escrow.
How Interest Rates Affect Affordability
Even a small change in interest rates can have a massive impact on your monthly budget. For example, on a $300,000 loan, the difference between a 6% and a 7% interest rate can increase your monthly payment by nearly $200. It is essential to shop around for the best rate and maintain a good credit score to qualify for favorable terms.
Using This Calculator
To get the most accurate result, input your expected Home Price and Down Payment. Don't forget to estimate your annual property taxes and insurance premiums, as these can add several hundred dollars to your monthly obligation. If you are buying a condo or a home in a planned community, include the HOA Fees to ensure your budget is realistic.
function calculateMortgage() {
// 1. Get Input Values
var homePrice = parseFloat(document.getElementById('mcHomePrice').value);
var downPayment = parseFloat(document.getElementById('mcDownPayment').value);
var interestRate = parseFloat(document.getElementById('mcInterestRate').value);
var loanTermYears = parseFloat(document.getElementById('mcLoanTerm').value);
var annualTax = parseFloat(document.getElementById('mcPropertyTax').value);
var annualInsurance = parseFloat(document.getElementById('mcInsurance').value);
var monthlyHOA = parseFloat(document.getElementById('mcHoaFees').value);
// 2. Validate Inputs
if (isNaN(homePrice) || homePrice <= 0) homePrice = 0;
if (isNaN(downPayment) || downPayment < 0) downPayment = 0;
if (isNaN(interestRate) || interestRate < 0) interestRate = 0;
if (isNaN(loanTermYears) || loanTermYears <= 0) loanTermYears = 30; // Default to 30 if invalid
if (isNaN(annualTax) || annualTax < 0) annualTax = 0;
if (isNaN(annualInsurance) || annualInsurance < 0) annualInsurance = 0;
if (isNaN(monthlyHOA) || monthlyHOA = home price
if (principal < 0) principal = 0;
var monthlyInterestRate = (interestRate / 100) / 12;
var numberOfPayments = loanTermYears * 12;
// Calculate Monthly Principal & Interest (P&I)
var monthlyPI = 0;
if (interestRate === 0) {
monthlyPI = principal / numberOfPayments;
} else {
// M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var pow = Math.pow(1 + monthlyInterestRate, numberOfPayments);
if (pow === 0 || !isFinite(pow)) {
monthlyPI = 0;
} else {
monthlyPI = principal * ((monthlyInterestRate * pow) / (pow – 1));
}
}
// Calculate Monthly Tax and Insurance
var monthlyTax = annualTax / 12;
var monthlyInsurance = annualInsurance / 12;
// Total Monthly Payment
var totalMonthlyPayment = monthlyPI + monthlyTax + monthlyInsurance + monthlyHOA;
// 4. Update UI
// Helper to format currency
var formatCurrency = function(num) {
return "$" + num.toLocaleString('en-US', { minimumFractionDigits: 2, maximumFractionDigits: 2 });
};
document.getElementById('mcResultPI').innerText = formatCurrency(monthlyPI);
document.getElementById('mcResultTax').innerText = formatCurrency(monthlyTax);
document.getElementById('mcResultIns').innerText = formatCurrency(monthlyInsurance);
document.getElementById('mcResultHOA').innerText = formatCurrency(monthlyHOA);
document.getElementById('mcTotalMonthly').innerText = formatCurrency(totalMonthlyPayment);
// Show results section
document.getElementById('mc-result-section').style.display = 'block';
}