Please enter valid numeric values for Home Price, Down Payment, Term, and Rate.
Monthly Payment Breakdown
Principal & Interest:$0.00
Property Tax:$0.00
Home Insurance:$0.00
HOA Fees:$0.00
Total Monthly Payment:$0.00
Loan Summary:
Loan Amount:
Total Interest Paid:
Payoff Date:
function calculateMortgage() {
// Get Input Values
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) || 0;
var homeInsuranceAnnual = parseFloat(document.getElementById('homeInsurance').value) || 0;
var hoaFeesMonthly = parseFloat(document.getElementById('hoaFees').value) || 0;
var errorMsg = document.getElementById('errorMsg');
var resultBox = document.getElementById('resultBox');
// Validation
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(loanTermYears) || isNaN(interestRateAnnual) || homePrice <= 0 || loanTermYears <= 0) {
errorMsg.style.display = 'block';
resultBox.style.display = 'none';
return;
}
errorMsg.style.display = 'none';
// Calculation Logic
var principal = homePrice – downPayment;
var monthlyInterestRate = (interestRateAnnual / 100) / 12;
var numberOfPayments = loanTermYears * 12;
var monthlyPI = 0;
// If interest rate is 0, simple division
if (interestRateAnnual === 0) {
monthlyPI = principal / numberOfPayments;
} else {
// Standard Amortization Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
monthlyPI = principal * ( (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1) );
}
var monthlyTax = propertyTaxAnnual / 12;
var monthlyInsurance = homeInsuranceAnnual / 12;
var totalMonthlyPayment = monthlyPI + monthlyTax + monthlyInsurance + hoaFeesMonthly;
var totalRepayment = monthlyPI * numberOfPayments;
var totalInterest = totalRepayment – principal;
// Date Calculation
var today = new Date();
var payoffDate = new Date(today.setMonth(today.getMonth() + numberOfPayments));
var monthNames = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
var payoffString = monthNames[payoffDate.getMonth()] + " " + payoffDate.getFullYear();
// Formatting Helper
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
// Update DOM
document.getElementById('resPI').innerText = formatter.format(monthlyPI);
document.getElementById('resTax').innerText = formatter.format(monthlyTax);
document.getElementById('resIns').innerText = formatter.format(monthlyInsurance);
document.getElementById('resHOA').innerText = formatter.format(hoaFeesMonthly);
document.getElementById('resTotal').innerText = formatter.format(totalMonthlyPayment);
document.getElementById('resLoanAmount').innerText = formatter.format(principal);
document.getElementById('resTotalInterest').innerText = formatter.format(totalInterest);
document.getElementById('resPayoffDate').innerText = payoffString;
resultBox.style.display = 'block';
}
Understanding Your Mortgage Calculation
Buying a home is one of the most significant financial decisions you will make in your lifetime. Understanding exactly how your monthly payments are calculated is crucial for budgeting and ensuring long-term financial stability. This mortgage calculator breaks down the costs associated with owning a home, going beyond just the loan repayment.
The Components of a Monthly Mortgage Payment (PITI)
Mortgage professionals often refer to your monthly payment as PITI, which stands for Principal, Interest, Taxes, and Insurance. Here is what each component means for your wallet:
Principal: This is the portion of your payment that goes directly toward paying down the loan balance (the amount you borrowed). In the early years of a mortgage, this amount is small, but it grows over time.
Interest: This is the cost of borrowing money paid to the lender. On a standard amortization schedule, interest makes up the majority of your payment in the beginning of the loan term.
Taxes: Property taxes are assessed by your local government to fund public services. Lenders typically collect 1/12th of your annual tax bill every month and hold it in an escrow account to pay on your behalf.
Insurance: Homeowners insurance protects your property against damage. Like taxes, this is usually collected monthly and held in escrow. If you put down less than 20%, you may also pay Private Mortgage Insurance (PMI).
How Interest Rates Affect Buying Power
The interest rate plays a massive role in your monthly payment and the total cost of the loan. Even a small difference, such as 0.5%, can save or cost you tens of thousands of dollars over the life of a 30-year loan.
Example Calculation
Consider a home price of $400,000 with a 20% down payment ($80,000). This leaves a loan amount of $320,000.
Interest Rate: 6.5%
Loan Term: 30 Years
Property Tax: $5,000/year
Insurance: $1,200/year
Using the calculator above, the Principal & Interest alone would be approximately $2,022. Adding in monthly taxes ($416) and insurance ($100), the total monthly obligation rises to roughly $2,538.
Why Include HOA Fees?
If you are buying a condo or a home in a planned community, you likely have to pay Homeowners Association (HOA) fees. While these are rarely paid to the mortgage lender, they are a mandatory monthly housing expense that affects your debt-to-income ratio and overall affordability.