function calculateMortgage() {
// Get Inputs
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);
// Validation
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm)) {
alert("Please enter valid numbers for all fields.");
return;
}
// Calculations
var principal = homePrice – downPayment;
var monthlyRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
// Principal & Interest Logic
var monthlyPI = 0;
if (interestRate === 0) {
monthlyPI = principal / numberOfPayments;
} else {
monthlyPI = (principal * monthlyRate) / (1 – Math.pow(1 + monthlyRate, -numberOfPayments));
}
// Tax and Insurance
var monthlyTax = 0;
if (!isNaN(propertyTax)) {
monthlyTax = propertyTax / 12;
}
var monthlyIns = 0;
if (!isNaN(homeInsurance)) {
monthlyIns = homeInsurance / 12;
}
var totalMonthly = monthlyPI + monthlyTax + monthlyIns;
// Update DOM
document.getElementById('totalMonthlyPayment').innerHTML = "$" + totalMonthly.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('principalInterest').innerHTML = "$" + monthlyPI.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('taxMonthly').innerHTML = "$" + monthlyTax.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('insMonthly').innerHTML = "$" + monthlyIns.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
}
// Initialize on load
window.onload = function() {
calculateMortgage();
};
Understanding Your Mortgage: A Comprehensive Guide
Purchasing a home is one of the most significant financial decisions you will make in your lifetime. While the listing price of a home gives you a baseline, the true cost of homeownership is reflected in your monthly mortgage payment. Using a specialized Mortgage Payment Calculator helps you accurately estimate these costs, ensuring you stay within your budget.
What is Included in a Mortgage Payment?
Most borrowers focus on the principal and interest, but a realistic monthly payment often includes other costs. This is commonly referred to as PITI:
Principal: The portion of your payment that goes toward reducing the loan balance.
Interest: The cost of borrowing money from your lender, calculated as a percentage of the remaining principal.
Taxes: Property taxes assessed by your local government, typically held in escrow by the lender and paid annually.
Insurance: Homeowners insurance protects your property against damage. Like taxes, this is often paid monthly into an escrow account.
How Interest Rates Affect Your Payment
Even a small fluctuation in interest rates can drastically change your monthly obligation. For example, on a $300,000 loan, a difference of just 1% in the interest rate can increase or decrease your monthly payment by hundreds of dollars. It is crucial to monitor current market rates and input accurate figures into the calculator to see how different scenarios impact your purchasing power.
The Impact of Your Down Payment
The size of your down payment directly influences your loan-to-value (LTV) ratio. A larger down payment reduces the principal loan amount, which lowers your monthly principal and interest payments. Additionally, putting down less than 20% often triggers Private Mortgage Insurance (PMI), an extra monthly fee not calculated in standard amortization schedules but vital to consider for affordability.
Fixed-Rate vs. Adjustable-Rate Mortgages
This calculator assumes a Fixed-Rate Mortgage, where the interest rate remains constant throughout the life of the loan (typically 15 or 30 years). This offers stability and predictability. Conversely, Adjustable-Rate Mortgages (ARMs) have rates that can fluctuate after an initial fixed period, potentially increasing your monthly costs significantly in the future.
Use the tool above to experiment with different home prices, down payments, and loan terms to find a mortgage plan that aligns with your long-term financial goals.