function calculateMortgage() {
// 1. Get Input Values
var price = parseFloat(document.getElementById('homePrice').value);
var down = parseFloat(document.getElementById('downPayment').value);
var years = parseFloat(document.getElementById('loanTerm').value);
var rate = parseFloat(document.getElementById('interestRate').value);
var taxYear = parseFloat(document.getElementById('propertyTax').value);
var insYear = parseFloat(document.getElementById('insurance').value);
var hoa = parseFloat(document.getElementById('hoaFees').value);
// Validate inputs
if (isNaN(price) || isNaN(down) || isNaN(years) || isNaN(rate)) {
alert("Please enter valid numbers for the core loan details.");
return;
}
// Handle optional fields getting NaN if empty
if (isNaN(taxYear)) taxYear = 0;
if (isNaN(insYear)) insYear = 0;
if (isNaN(hoa)) hoa = 0;
// 2. Perform Calculations
var principal = price – down;
var monthlyRate = rate / 100 / 12;
var numberOfPayments = years * 12;
// Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var monthlyPI = 0;
if (rate === 0) {
monthlyPI = principal / numberOfPayments;
} else {
monthlyPI = principal * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
}
// Monthly Taxes and Insurance
var monthlyTax = taxYear / 12;
var monthlyIns = insYear / 12;
// Total Monthly Payment
var totalMonthly = monthlyPI + monthlyTax + monthlyIns + hoa;
// 3. Update UI
document.getElementById('totalMonthly').innerText = "$" + totalMonthly.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('piResult').innerText = "$" + monthlyPI.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('taxResult').innerText = "$" + monthlyTax.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Combine Insurance and HOA for the summary view
var combinedInsHoa = monthlyIns + hoa;
document.getElementById('insResult').innerText = "$" + combinedInsHoa.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Show result section
document.getElementById('resultsArea').style.display = "block";
}
Mortgage Payment Calculator: Estimate Your Monthly Costs
Buying a home is often the largest financial decision a person will make in their lifetime. Before you start touring open houses, it is crucial to understand exactly how much you can afford. Our Mortgage Payment Calculator is designed to give you a comprehensive view of your potential housing costs, going beyond just the sticker price of the home.
How Your Monthly Mortgage Payment is Calculated
Most first-time homebuyers focus solely on the principal and interest payment, but your actual monthly obligation usually includes four key components, often referred to as PITI:
Principal: The portion of your payment that goes toward paying down the loan balance (the home price minus your down payment).
Interest: The cost of borrowing money from the lender. In the early years of a 30-year mortgage, the majority of your payment goes toward interest.
Taxes: Property taxes assessed by your local government. These are usually held in an escrow account by your lender and paid annually.
Insurance: Homeowner's insurance protects your property against damage. Like taxes, this is often divided into monthly installments and paid via escrow.
Understanding the Variables
Down Payment Impact
The size of your down payment significantly affects your monthly costs. A larger down payment reduces the principal loan amount, which lowers your monthly P&I (Principal & Interest) payment. Additionally, if you put down less than 20% of the home's value, lenders often require Private Mortgage Insurance (PMI), which is an extra cost not included in the standard calculation above.
Interest Rate Volatility
Even a small change in interest rates can drastically change the affordability of a home. For example, on a $400,000 loan, the difference between a 6% rate and a 7% rate is roughly $260 per month. Use this calculator to stress-test your budget against different rate scenarios.
Loan Term: 15-Year vs. 30-Year
The "Loan Term" is the duration over which you agree to repay the loan.
30-Year Fixed: The most popular option. It offers lower monthly payments but results in significantly more interest paid over the life of the loan.
15-Year Fixed: This option comes with higher monthly payments, but you build equity much faster and pay far less in total interest.
How to Use This Tool for Budgeting
To get the most accurate estimate, try to find the current property tax rate in your desired county (usually between 0.5% and 2.5% of the property value) and estimate your homeowner's insurance costs (roughly $1,000 to $2,000 per year for average homes). Don't forget to include HOA fees if you are looking at condos or planned communities, as these are paid directly to the association and affect your debt-to-income ratio.