Calculating your potential monthly mortgage payment is a crucial first step in the home buying process. This Mortgage Payment Calculator helps you estimate your monthly financial obligation by factoring in not just the loan repayment, but also necessary costs like property taxes, homeowner's insurance, and HOA fees.
Your monthly payment is primarily composed of Principal and Interest (P&I). The Principal is the money you borrowed to buy the home, while the Interest is the cost charged by the lender for borrowing that money. In the early years of a standard fixed-rate mortgage, the majority of your payment goes toward interest, gradually shifting toward principal as the loan matures.
How Interest Rates Affect Your Loan
The interest rate plays a massive role in the affordability of a home. Even a small fluctuation of 0.5% can significantly change your monthly payment and the total amount of interest paid over the life of the loan. For example, on a $300,000 loan, the difference between a 6% and a 7% interest rate can amount to hundreds of dollars per month and tens of thousands over 30 years.
Additional Costs: Taxes and Insurance
Many first-time homebuyers focus solely on the mortgage loan but forget about escrow costs. Most lenders require you to pay 1/12th of your estimated annual Property Taxes and Homeowner's Insurance premiums into an escrow account every month. This calculator includes these inputs to provide a realistic "out-the-door" monthly cost, rather than just the loan repayment figure.
HOA Fees
If you are buying a condo or a home in a planned community, you likely have to pay Homeowner Association (HOA) fees. These are typically paid directly to the association, but they are a mandatory monthly cost that affects your Debt-to-Income (DTI) ratio. Always include these in your calculation to ensure the home fits within your budget.
function formatCurrency(num) {
return "$" + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
function calculateMortgage() {
// 1. Get Input Values
var price = document.getElementById("homePrice").value;
var down = document.getElementById("downPayment").value;
var rateInput = document.getElementById("interestRate").value;
var termYears = document.getElementById("loanTerm").value;
var taxYear = document.getElementById("propertyTax").value;
var insYear = document.getElementById("homeInsurance").value;
var hoaMonth = document.getElementById("hoaFees").value;
// 2. Validate Inputs
if (price === "" || down === "" || rateInput === "" || termYears === "") {
document.getElementById("errorDisplay").style.display = "block";
document.getElementById("resultsArea").style.display = "none";
return;
}
// Convert to numbers
var P = parseFloat(price) – parseFloat(down); // Principal
var annualRate = parseFloat(rateInput);
var r = annualRate / 100 / 12; // Monthly interest rate
var n = parseFloat(termYears) * 12; // Total number of months
var taxMonthly = parseFloat(taxYear) / 12;
var insMonthly = parseFloat(insYear) / 12;
var hoa = parseFloat(hoaMonth);
if (isNaN(P) || isNaN(r) || isNaN(n)) {
document.getElementById("errorDisplay").style.display = "block";
return;
} else {
document.getElementById("errorDisplay").style.display = "none";
}
// 3. Calculation Logic
var monthlyPI = 0;
// If interest rate is 0, just divide principal by months
if (annualRate === 0) {
monthlyPI = P / n;
} else {
// Standard Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
monthlyPI = P * (r * Math.pow(1 + r, n)) / (Math.pow(1 + r, n) – 1);
}
var totalMonthly = monthlyPI + taxMonthly + insMonthly + hoa;
var totalInterest = (monthlyPI * n) – P;
// 4. Update Results
document.getElementById("resultsArea").style.display = "block";
document.getElementById("totalMonthlyPayment").innerHTML = formatCurrency(totalMonthly);
document.getElementById("resultPI").innerHTML = formatCurrency(monthlyPI);
document.getElementById("resultTax").innerHTML = formatCurrency(taxMonthly);
document.getElementById("resultIns").innerHTML = formatCurrency(insMonthly);
document.getElementById("resultHOA").innerHTML = formatCurrency(hoa);
document.getElementById("resultLoanAmount").innerHTML = formatCurrency(P);
document.getElementById("resultTotalInterest").innerHTML = formatCurrency(totalInterest);
}