Estimate your monthly payments and total interest costs.
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$
%
$
$
$
Estimated Monthly Payment
$0.00
Principal & Interest
$0.00
Total Interest
$0.00
Total Cost of Loan
$0.00
*Includes Tax: $0 | Insurance: $0 | HOA: $0
function calculateMortgage() {
// Retrieve inputs strictly by ID
var homePrice = parseFloat(document.getElementById("homePrice").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var loanTermYears = parseFloat(document.getElementById("loanTerm").value);
var interestRateAnnual = parseFloat(document.getElementById("interestRate").value);
var propertyTaxAnnual = parseFloat(document.getElementById("propertyTax").value);
var homeInsuranceAnnual = parseFloat(document.getElementById("homeInsurance").value);
var hoaFeesMonthly = parseFloat(document.getElementById("hoaFees").value);
// Validation
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(loanTermYears) || isNaN(interestRateAnnual)) {
alert("Please enter valid numbers for the required fields.");
return;
}
// Logic
var principal = homePrice – downPayment;
// Edge case: Negative principal
if (principal <= 0) {
alert("Down payment cannot be greater than or equal to Home Price.");
return;
}
var monthlyInterestRate = (interestRateAnnual / 100) / 12;
var numberOfPayments = loanTermYears * 12;
// Calculate Principal & Interest (P&I)
// Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var monthlyPI = 0;
if (interestRateAnnual === 0) {
monthlyPI = principal / numberOfPayments;
} else {
var mathPower = Math.pow(1 + monthlyInterestRate, numberOfPayments);
monthlyPI = principal * ((monthlyInterestRate * mathPower) / (mathPower – 1));
}
// Additional Monthly Costs
var monthlyTax = propertyTaxAnnual / 12;
var monthlyInsurance = homeInsuranceAnnual / 12;
// Total Monthly Payment
var totalMonthly = monthlyPI + monthlyTax + monthlyInsurance + hoaFeesMonthly;
// Total Loan Metrics
var totalPaidOverTerm = monthlyPI * numberOfPayments;
var totalInterestPaid = totalPaidOverTerm – principal;
// Display Results
document.getElementById("totalMonthlyPayment").innerText = "$" + totalMonthly.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("piPayment").innerText = "$" + monthlyPI.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalInterest").innerText = "$" + totalInterestPaid.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 0});
document.getElementById("totalCost").innerText = "$" + totalPaidOverTerm.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 0});
document.getElementById("monthlyTax").innerText = "$" + monthlyTax.toFixed(0);
document.getElementById("monthlyIns").innerText = "$" + monthlyInsurance.toFixed(0);
document.getElementById("monthlyHoa").innerText = "$" + hoaFeesMonthly.toFixed(0);
// Show result container
document.getElementById("results").style.display = "block";
}
Understanding Your Mortgage Calculation
Buying a home is likely the largest financial commitment you will make in your lifetime. Understanding how your monthly mortgage payment is calculated is essential for budgeting and determining exactly how much house you can afford. Our Mortgage Calculator breaks down the costs associated with homeownership, moving beyond just the loan repayment to include taxes, insurance, and fees.
The Components of a Monthly Mortgage Payment (PITI)
Lenders often refer to your monthly payment as PITI, which stands for:
Principal: The portion of your payment that goes toward paying down the original loan amount. In the early years of a standard amortization schedule, this amount is small but grows over time.
Interest: The fee charged by the lender for borrowing the money. Interest payments are highest at the start of the loan term.
Taxes: Property taxes assessed by your local government. These are often collected by the lender and held in an escrow account.
Insurance: Homeowners insurance protects your property against damage. Like taxes, this is often escrowed into your monthly payment.
How Interest Rates Affect Your Buying Power
Even a small difference in interest rates can have a massive impact on your monthly payment and the total cost of the loan. For example, on a $300,000 loan, a 1% increase in interest rate can increase your monthly payment by approximately $180 and cost you over $60,000 in additional interest over the life of a 30-year loan.
Frequently Asked Questions
What is Private Mortgage Insurance (PMI)?
If your down payment is less than 20% of the home price, lenders typically require you to pay Private Mortgage Insurance. This protects the lender if you default. PMI is an additional cost not included in the standard Principal and Interest calculation but is a critical factor for low-down-payment loans.
Should I choose a 15-year or 30-year term?
A 30-year mortgage offers lower monthly payments, making homes more affordable month-to-month, but you will pay significantly more in interest over the life of the loan. A 15-year mortgage has higher monthly payments but allows you to build equity faster and save thousands in interest costs.
How do HOA fees impact my mortgage?
Homeowners Association (HOA) fees are paid directly to the association, not your lender, but lenders factor them into your Debt-to-Income (DTI) ratio. High HOA fees can reduce the loan amount you qualify for.