function calculateMortgage() {
// 1. 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 = parseFloat(document.getElementById('loanTerm').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) || isNaN(down) || isNaN(rate) || isNaN(years)) {
alert("Please enter valid numbers for Home Price, Down Payment, Interest Rate, and Loan Term.");
return;
}
// Handle optional fields if empty
if (isNaN(annualTax)) annualTax = 0;
if (isNaN(annualIns)) annualIns = 0;
if (isNaN(monthlyHOA)) monthlyHOA = 0;
// 3. Core Calculations
var principal = price – down;
var monthlyRate = (rate / 100) / 12;
var totalPayments = years * 12;
// Calculate Principal & Interest (P&I)
var monthlyPI = 0;
if (rate === 0) {
monthlyPI = principal / totalPayments;
} else {
monthlyPI = principal * (monthlyRate * Math.pow(1 + monthlyRate, totalPayments)) / (Math.pow(1 + monthlyRate, totalPayments) – 1);
}
var monthlyTax = annualTax / 12;
var monthlyIns = annualIns / 12;
var totalMonthlyPayment = monthlyPI + monthlyTax + monthlyIns + monthlyHOA;
var totalCostOfLoan = (monthlyPI * totalPayments);
var totalInterest = totalCostOfLoan – principal;
// Calculate Payoff Date
var today = new Date();
today.setMonth(today.getMonth() + totalPayments);
var options = { month: 'long', year: 'numeric' };
var payoffDate = today.toLocaleDateString("en-US", options);
// 4. Update UI
// Helper for currency formatting
var fmt = new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' });
document.getElementById('piDisplay').innerText = fmt.format(monthlyPI);
document.getElementById('taxDisplay').innerText = fmt.format(monthlyTax);
document.getElementById('insDisplay').innerText = fmt.format(monthlyIns);
document.getElementById('hoaDisplay').innerText = fmt.format(monthlyHOA);
document.getElementById('monthlyTotalDisplay').innerText = fmt.format(totalMonthlyPayment);
document.getElementById('totalInterestDisplay').innerText = fmt.format(totalInterest);
document.getElementById('payoffDateDisplay').innerText = payoffDate;
// Show results container
document.getElementById('resultsArea').style.display = 'block';
}
Understanding Your Mortgage Estimate
Buying a home is one of the largest financial decisions you will ever make. Our Mortgage Calculator is designed to give you a clear, comprehensive view of what your monthly housing costs will actually look like. Unlike basic calculators that only show principal and interest, this tool factors in the real-world costs of Property Taxes, Homeowners Insurance, and HOA fees—collectively known as PITI.
What is PITI?
Lenders use the acronym PITI to describe the four main components of your monthly mortgage bill:
Principal: The portion of your payment that goes toward paying down the loan balance ($Home Price minus $Down Payment).
Interest: The cost of borrowing money from the lender, determined by your annual percentage rate (APR).
Taxes: Property taxes assessed by your local government, usually paid into an escrow account monthly.
Insurance: Homeowners insurance protects your property from damage and is typically required by lenders.
How Interest Rates Impact Your Payment
Even a small change in interest rates can significantly affect your monthly payment and the total amount you pay over the life of the loan. For example, on a $300,000 loan, a 1% increase in interest rate can raise your monthly payment by hundreds of dollars and increase your total interest paid by over $60,000 over 30 years. Use the calculator above to scenario-test different rates.
Strategies to Lower Your Mortgage Payment
If the calculated monthly payment is higher than your budget allows, consider these strategies:
Increase Your Down Payment: Putting more money down reduces the principal loan amount and may eliminate the need for Private Mortgage Insurance (PMI).
Extend the Loan Term: Switching from a 15-year to a 30-year term will lower monthly payments, though you will pay more in total interest over the long run.
Shop for Lower Insurance: Homeowners insurance premiums vary wildly; shopping around can save you money on your monthly escrow requirements.
Frequently Asked Questions
Does this calculator include PMI?
This specific calculator focuses on PITI and HOA. If your down payment is less than 20% of the home price, lenders usually require Private Mortgage Insurance (PMI). PMI typically costs between 0.5% and 1% of the loan amount annually. You can add this estimated cost to the "Annual Home Insurance" field for a rough estimate if you expect to pay PMI.
What is a good debt-to-income (DTI) ratio?
Lenders look at your DTI to determine if you can afford the monthly payments. Generally, lenders prefer that your total monthly debts (including your new mortgage) do not exceed 36% to 43% of your gross monthly income.