Please enter valid positive numbers for all fields.
Estimated Monthly Payment
Principal & Interest
Property Tax
Home Insurance
HOA Fees
Loan Amount
Total Interest Paid
function calculateMortgage() {
// Retrieve 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);
var hoaFees = parseFloat(document.getElementById("hoaFees").value);
var errorMsg = document.getElementById("error-message");
var resultDiv = document.getElementById("calc-result");
// Basic Validation
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm) ||
isNaN(propertyTax) || isNaN(homeInsurance) || isNaN(hoaFees) ||
homePrice < 0 || downPayment < 0 || interestRate = homePrice) {
errorMsg.innerText = "Down payment cannot exceed home price.";
errorMsg.style.display = "block";
resultDiv.style.display = "none";
return;
} else {
errorMsg.innerText = "Please enter valid positive numbers for all fields.";
errorMsg.style.display = "none";
}
// Mortgage Calculation
var loanAmount = homePrice – downPayment;
var annualRate = interestRate / 100;
var monthlyRate = annualRate / 12;
var numberOfPayments = loanTerm * 12;
var monthlyPI = 0;
// Handle zero interest rate case
if (interestRate === 0) {
monthlyPI = loanAmount / numberOfPayments;
} else {
// Standard Amortization 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 Escrow components
var monthlyTax = propertyTax / 12;
var monthlyInsurance = homeInsurance / 12;
// Total Monthly Payment
var totalMonthlyPayment = monthlyPI + monthlyTax + monthlyInsurance + hoaFees;
// Total Cost metrics
var totalPaymentOverLife = monthlyPI * numberOfPayments;
var totalInterest = totalPaymentOverLife – loanAmount;
// Formatting Currency
var currencyFormat = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
// Update DOM
document.getElementById("totalMonthly").innerText = currencyFormat.format(totalMonthlyPayment);
document.getElementById("piAmount").innerText = currencyFormat.format(monthlyPI);
document.getElementById("taxAmount").innerText = currencyFormat.format(monthlyTax);
document.getElementById("insAmount").innerText = currencyFormat.format(monthlyInsurance);
document.getElementById("hoaAmount").innerText = currencyFormat.format(hoaFees);
document.getElementById("loanAmountResult").innerText = currencyFormat.format(loanAmount);
document.getElementById("totalInterestResult").innerText = currencyFormat.format(totalInterest);
// Show result
resultDiv.style.display = "block";
}
Understanding Your Mortgage Payment
Buying a home is often the largest financial investment a person will make in their lifetime. Understanding exactly how your monthly mortgage payment is calculated is crucial for maintaining a healthy budget and ensuring long-term financial stability. Our Advanced Mortgage Payment Calculator breaks down the complexities of home financing into clear, actionable data.
The Four Pillars of a Mortgage Payment (PITI)
Most homeowners are surprised to learn that their "mortgage check" covers more than just the loan repayment. The industry standard acronym PITI explains the four primary components:
Principal: The portion of your payment that goes directly toward reducing the loan balance. In the early years of a loan, this amount is small, but it grows over time.
Interest: The cost of borrowing money. Initially, the majority of your payment goes toward interest.
Taxes: Property taxes assessed by your local government. These are often collected by the lender into an escrow account and paid annually on your behalf.
Insurance: Homeowners insurance protects your property against damage. Like taxes, this is usually part of your monthly escrow payment.
How Interest Rates Affect Affordability
Even a small fluctuation in interest rates can significantly impact your purchasing power. For example, on a $300,000 loan, the difference between a 6.0% rate and a 7.0% rate can increase your monthly payment by nearly $200 and cost you tens of thousands of dollars in additional interest over the life of a 30-year loan.
The Impact of Loan Term
Choosing between a 15-year and a 30-year fixed mortgage is a common dilemma. A 30-year term offers lower monthly payments, making the home more affordable on a month-to-month basis. However, you will pay significantly more in total interest. Conversely, a 15-year term comes with higher monthly payments but allows you to build equity faster and save a substantial amount on interest.
Don't Forget HOA Fees
If you are buying a condo or a home in a planned community, Homeowners Association (HOA) fees are a critical factor. Unlike taxes and insurance, HOA fees are rarely included in the mortgage loan itself but are a mandatory monthly expense that lenders count against your debt-to-income ratio. Our calculator includes a dedicated field for HOA fees to ensure your total monthly estimate is accurate.
Using This Calculator
To get the most accurate result, try to find the exact property tax rate for the specific county where you are looking to buy, as this can vary wildly from 0.5% to over 2.5% of the home's value annually. By inputting realistic numbers for insurance and HOA fees, you can confidently determine your "walk-away" price and shop for homes that truly fit your budget.