Calculating your monthly mortgage payment is the first critical step in the home buying process. This tool helps you estimate your total monthly housing costs, also known as PITI (Principal, Interest, Taxes, and Insurance), ensuring you stay within your budget.
How is the Monthly Payment Calculated?
Your monthly payment is composed of several factors:
Principal: The portion of your payment that goes toward reducing the loan balance.
Interest: The fee charged by the lender for borrowing the money. Early in your loan term, a larger portion of your payment goes toward interest.
Property Taxes: Assessed by your local government, usually bundled into your monthly payment and held in escrow.
Homeowner's Insurance: Protects your property against damage. Lenders require this to protect their investment.
HOA Fees: If you buy a condo or a home in a managed community, you may pay Homeowner Association fees. These are usually paid directly to the association but affect your monthly affordability.
The Impact of Interest Rates on Your Loan
Even a small difference in interest rates can significantly impact your monthly payment and the total cost of the loan. For example, on a $300,000 loan, a 1% increase in interest rate can increase your monthly payment by hundreds of dollars and your total interest paid by over $60,000 over the life of a 30-year loan.
30-Year vs. 15-Year Mortgage Terms
This calculator allows you to adjust the loan term. A 30-year term offers lower monthly payments but results in higher total interest paid. A 15-year term has higher monthly payments but allows you to build equity faster and save significantly on interest costs.
What is PMI?
If your down payment is less than 20% of the home price, lenders often require Private Mortgage Insurance (PMI). While this calculator focuses on PITI and HOA, remember to budget an extra 0.5% to 1% of the loan amount annually if you are putting down less than 20%.
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 annualRate = parseFloat(document.getElementById("interestRate").value);
var annualTax = parseFloat(document.getElementById("propertyTax").value);
var annualIns = parseFloat(document.getElementById("homeInsurance").value);
var monthlyHOA = parseFloat(document.getElementById("hoaFees").value);
// 2. Validation
if (isNaN(price) || price <= 0) {
alert("Please enter a valid Home Price.");
return;
}
if (isNaN(down) || down < 0) {
down = 0;
}
if (isNaN(termYears) || termYears <= 0) {
alert("Please enter a valid Loan Term.");
return;
}
if (isNaN(annualRate) || annualRate < 0) {
alert("Please enter a valid Interest Rate.");
return;
}
if (isNaN(annualTax)) annualTax = 0;
if (isNaN(annualIns)) annualIns = 0;
if (isNaN(monthlyHOA)) monthlyHOA = 0;
// 3. Core Calculations
var loanAmount = price – down;
// Handle case where down payment is greater than price
if (loanAmount 0 && monthlyRate > 0) {
var x = Math.pow(1 + monthlyRate, totalPayments);
monthlyPrincipalInterest = (loanAmount * x * monthlyRate) / (x – 1);
} else if (loanAmount > 0 && monthlyRate === 0) {
// 0% interest case
monthlyPrincipalInterest = loanAmount / totalPayments;
}
var monthlyTax = annualTax / 12;
var monthlyIns = annualIns / 12;
var totalMonthlyPayment = monthlyPrincipalInterest + monthlyTax + monthlyIns + monthlyHOA;
var totalInterest = (monthlyPrincipalInterest * totalPayments) – loanAmount;
if (totalInterest < 0) totalInterest = 0;
// 4. Formatting Helper
function formatMoney(num) {
return "$" + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
// 5. Update DOM
document.getElementById("totalMonthlyPayment").innerHTML = formatMoney(totalMonthlyPayment);
document.getElementById("resPrincipalInterest").innerHTML = formatMoney(monthlyPrincipalInterest);
document.getElementById("resTax").innerHTML = formatMoney(monthlyTax);
document.getElementById("resIns").innerHTML = formatMoney(monthlyIns);
document.getElementById("resHOA").innerHTML = formatMoney(monthlyHOA);
document.getElementById("resLoanAmount").innerHTML = formatMoney(loanAmount);
document.getElementById("resTotalInterest").innerHTML = formatMoney(totalInterest);
// Show results
document.getElementById("resultsArea").style.display = "block";
}