function calculateMortgage() {
var homeValue = parseFloat(document.getElementById("homeValue").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 errorMsg = document.getElementById("errorMsg");
var resultBox = document.getElementById("resultBox");
// Basic Validation
if (isNaN(homeValue) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm) || homeValue < 0 || interestRate < 0 || loanTerm <= 0) {
errorMsg.style.display = "block";
resultBox.style.display = "none";
return;
}
// Default 0 for optional fields if empty/NaN
if (isNaN(propertyTax)) propertyTax = 0;
if (isNaN(homeInsurance)) homeInsurance = 0;
errorMsg.style.display = "none";
// Calculations
var loanAmount = homeValue – downPayment;
var monthlyRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
var monthlyPI = 0;
// Handle 0% interest case
if (interestRate === 0) {
monthlyPI = loanAmount / numberOfPayments;
} else {
// Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
monthlyPI = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
}
// Monthly Taxes and Insurance
var monthlyTax = propertyTax / 12;
var monthlyIns = homeInsurance / 12;
var totalMonthly = monthlyPI + monthlyTax + monthlyIns;
// Totals
var totalPaid = monthlyPI * numberOfPayments;
var totalInterest = totalPaid – loanAmount;
// Display Results
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 = "$" + monthlyIns.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resTotal").innerText = "$" + totalMonthly.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resTotalInt").innerText = "$" + totalInterest.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resTotalCost").innerText = "$" + (totalPaid + (monthlyTax * numberOfPayments) + (monthlyIns * numberOfPayments)).toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
resultBox.style.display = "block";
}
Understanding Your Mortgage Calculation
Purchasing a home is one of the most significant financial decisions you will make. Using a mortgage calculator helps you understand exactly how much you can expect to pay each month, allowing for better budget planning. This tool breaks down your payments into principal, interest, taxes, and insurance (often referred to as PITI).
Key Components of Your Monthly Payment
Principal: The portion of your payment that goes directly toward paying down the loan balance. In the early years of a mortgage, this amount is typically smaller than the interest portion.
Interest: The cost of borrowing money from your lender. The higher your interest rate, the more you pay over the life of the loan.
Property Taxes: Taxes assessed by your local government based on the value of your property. These are often divided by 12 and collected monthly by your lender in an escrow account.
Homeowners Insurance: Protection for your property against damages. Lenders require this coverage, and like taxes, the premiums are often bundled into your monthly mortgage payment.
How Interest Rates Affect Your Payment
Even a small fluctuation in interest rates can drastically change your monthly obligation and the total cost of your home. For example, on a $300,000 loan, a difference of just 1% in the interest rate can result in tens of thousands of dollars in extra interest paid over a 30-year term. It is crucial to shop around for the best rate and maintain a good credit score to secure favorable terms.
Choosing the Right Loan Term
Most homebuyers choose between a 15-year and a 30-year mortgage. A 30-year term offers lower monthly payments, making the home more affordable month-to-month, but you will pay significantly more in interest over the life of the loan. Conversely, a 15-year term has higher monthly payments but allows you to build equity faster and save money on total interest costs.
{
"@context": "https://schema.org",
"@type": "FAQPage",
"mainEntity": [{
"@type": "Question",
"name": "How is a mortgage payment calculated?",
"acceptedAnswer": {
"@type": "Answer",
"text": "A mortgage payment is calculated using the loan amount, interest rate, and loan term. The standard formula determines the monthly principal and interest. Additionally, annual property taxes and homeowners insurance are often divided by 12 and added to this amount to determine the total monthly payment."
}
}, {
"@type": "Question",
"name": "Does this calculator include PMI?",
"acceptedAnswer": {
"@type": "Answer",
"text": "This calculator focuses on Principal, Interest, Taxes, and Insurance. Private Mortgage Insurance (PMI) is typically required if your down payment is less than 20% of the home's value. While not explicitly separated here, you can estimate PMI costs and add them to your monthly budget or include them in the insurance field for a rough estimate."
}
}, {
"@type": "Question",
"name": "What is an amortization schedule?",
"acceptedAnswer": {
"@type": "Answer",
"text": "An amortization schedule is a table detailing each periodic payment on an amortizing loan. It shows the amount of principal and the amount of interest that comprise each payment until the loan is paid off at the end of its term. Early payments consist mostly of interest, while later payments are primarily principal."
}
}]
}