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 = parseInt(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) || isNaN(propertyTax) || isNaN(homeInsurance) || isNaN(hoaFees)) {
alert("Please enter valid numbers in all fields.");
return;
}
if (homePrice 0) {
var monthlyRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
if (interestRate === 0) {
monthlyPI = principal / numberOfPayments;
} else {
// Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var mathPow = Math.pow(1 + monthlyRate, numberOfPayments);
monthlyPI = (principal * monthlyRate * mathPow) / (mathPow – 1);
}
}
var monthlyTax = propertyTax / 12;
var monthlyInsurance = homeInsurance / 12;
var totalMonthlyPayment = monthlyPI + monthlyTax + monthlyInsurance + hoaFees;
// Formatting currency
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
// Update DOM
document.getElementById("totalPaymentDisplay").innerHTML = formatter.format(totalMonthlyPayment);
document.getElementById("piDisplay").innerHTML = formatter.format(monthlyPI);
document.getElementById("taxDisplay").innerHTML = formatter.format(monthlyTax);
document.getElementById("insDisplay").innerHTML = formatter.format(monthlyInsurance);
document.getElementById("hoaDisplay").innerHTML = formatter.format(hoaFees);
// Show result container
document.getElementById("result").style.display = "block";
}
Understanding Your Mortgage Calculator Results
Buying a home is one of the largest financial decisions you will make in your lifetime. Our Mortgage Payment Calculator is designed to provide you with a clear, accurate estimate of what your monthly housing costs will look like. Unlike basic calculators that only look at principal and interest, this tool accounts for the "PITI" (Principal, Interest, Taxes, and Insurance) plus HOA fees to give you a realistic budget.
The Components of Your Monthly Payment
Your monthly mortgage payment is composed of several distinct parts. Understanding these can help you better negotiate your loan and plan your finances:
Principal & Interest: This is the core of your loan. The principal pays down the balance you borrowed, while the interest is the cost of borrowing that money. In the early years of a standard amortization schedule, a larger portion of your payment goes toward interest.
Property Taxes: Local governments assess taxes on real estate to fund services like schools and roads. This calculator estimates the monthly portion of your annual tax bill, which is typically held in an escrow account by your lender.
Homeowners Insurance: Lenders require you to insure your home against damage. Like taxes, this is usually divided into monthly installments and paid via escrow.
HOA Fees: If you buy a condo or a home in a planned community, you may owe Homeowners Association dues. These are usually paid directly to the association, not the lender, but they affect your total monthly affordability.
How Interest Rates Impact Affordability
Even a small change in interest rates can significantly affect your buying power. For example, on a $300,000 loan, a 1% increase in interest rate can raise your monthly payment by hundreds of dollars. Use the "Interest Rate" field in the calculator to simulate different market conditions or loan offers to see how sensitive your budget is to rate fluctuations.
Choosing the Right Loan Term
The term of your loan dictates how long you will be paying it off. The most common term is 30 years, which offers lower monthly payments but results in higher total interest paid over the life of the loan. A 15-year term will have higher monthly payments, but you will build equity much faster and pay significantly less interest overall.
The Importance of the Down Payment
Your down payment reduces the principal amount you need to borrow. A larger down payment (typically 20% or more) not only lowers your monthly Principal & Interest payment but can also help you avoid Private Mortgage Insurance (PMI), a cost not included in this standard calculation but one that applies to many loans with less than 20% equity.