function calculateMortgage() {
// Get Input Values
var homePrice = parseFloat(document.getElementById("homePrice").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var propertyTax = parseFloat(document.getElementById("propertyTax").value);
var homeInsurance = parseFloat(document.getElementById("homeInsurance").value);
var hoaFees = parseFloat(document.getElementById("hoaFees").value);
// Validation
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm)) {
alert("Please enter valid numbers for the required fields.");
return;
}
// Handle empty optional fields
if (isNaN(propertyTax)) propertyTax = 0;
if (isNaN(homeInsurance)) homeInsurance = 0;
if (isNaN(hoaFees)) hoaFees = 0;
// Core Calculations
var loanAmount = homePrice – downPayment;
var monthlyRate = (interestRate / 100) / 12;
var totalPayments = loanTerm * 12;
var monthlyPI = 0;
// Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
if (interestRate === 0) {
monthlyPI = loanAmount / totalPayments;
} else {
var mathPower = Math.pow(1 + monthlyRate, totalPayments);
monthlyPI = loanAmount * ((monthlyRate * mathPower) / (mathPower – 1));
}
var monthlyTax = propertyTax / 12;
var monthlyInsurance = homeInsurance / 12;
var totalMonthly = monthlyPI + monthlyTax + monthlyInsurance + hoaFees;
// Update DOM
document.getElementById("resPI").innerText = "$" + monthlyPI.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resTax").innerText = "$" + monthlyTax.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resIns").innerText = "$" + monthlyInsurance.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resHOA").innerText = "$" + hoaFees.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resTotal").innerText = "$" + totalMonthly.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resLoanAmount").innerText = "$" + loanAmount.toLocaleString('en-US', {minimumFractionDigits: 0, maximumFractionDigits: 0});
// Show Results
document.getElementById("results").style.display = "block";
}
Understanding Your Mortgage Payment Components
When financing a home, the monthly check you write covers more than just the loan repayment. Understanding the "PITI" components—Principal, Interest, Taxes, and Insurance—is crucial for budgeting and determining exactly how much house you can afford.
1. Principal and Interest (P&I)
This is the core of your mortgage payment. The Principal pays down the loan balance, while the Interest is the cost of borrowing money from the lender.
Early Years: In a standard 30-year fixed mortgage, the majority of your early payments go toward interest.
Later Years: As the loan matures, a larger portion of the payment goes toward reducing the principal balance (amortization).
2. Property Taxes
Local governments levy taxes on real estate to fund public services like schools, police, and road maintenance. Lenders often collect this amount monthly, hold it in an escrow account, and pay the tax bill on your behalf when it is due.
SEO Tip: Property taxes vary significantly by location. While the national average is around 1.1%, some states have rates as high as 2.5% or as low as 0.3%. Always verify local millage rates when calculating affordability.
3. Homeowner's Insurance
Lenders require you to maintain hazard insurance to protect the collateral (your home) against damages from fire, storms, and theft. Like taxes, this premium is usually divided by 12 and added to your monthly mortgage payment.
4. HOA Fees
If you buy a condo or a home in a planned community, you may owe Homeowners Association (HOA) dues. While these are rarely paid through the lender (you usually pay the association directly), lenders factor this monthly obligation into your Debt-to-Income (DTI) ratio to ensure you qualify for the loan.
How Interest Rates Impact Affordability
Even a small change in interest rates can drastically alter your buying power. For example, on a $300,000 loan, the difference between a 6.0% rate and a 7.0% rate adds roughly $200 to your monthly payment and over $70,000 in total interest over 30 years.
Frequently Asked Questions
What is an escrow account?
An escrow account is a savings account managed by your mortgage servicer. A portion of your monthly payment is deposited here to cover property taxes and insurance premiums when they become due.
Does this calculator include PMI?
This specific calculator focuses on PITI and HOA. However, if your down payment is less than 20%, you should typically budget an additional 0.5% to 1.5% of the loan amount annually for Private Mortgage Insurance (PMI).
Should I choose a 15-year or 30-year term?
A 15-year mortgage usually offers a lower interest rate and significant interest savings over the life of the loan, but the monthly payments are considerably higher. A 30-year term offers lower monthly payments, providing more budget flexibility.