Please enter valid numeric values greater than zero for Home Price.
Total Monthly Payment:$0.00
Principal & Interest:$0.00
Property Taxes (Monthly):$0.00
Home Insurance (Monthly):$0.00
HOA Fees:$0.00
Loan Amount:$0.00
Total Interest Paid Over Term:$0.00
Total Cost of Loan:$0.00
Understanding Your Mortgage Calculation
Calculating your potential mortgage payment is a crucial first step in the home buying process. This calculator breaks down the "PITI" components of your payment: Principal, Interest, Taxes, and Insurance, along with any HOA fees.
Key Components of Your Monthly Payment
Principal: The portion of your payment that goes directly toward reducing your loan balance.
Interest: The cost of borrowing money from your lender, calculated based on your remaining balance and interest rate.
Property Taxes: Assessed by your local government to fund services like schools and infrastructure. This calculator estimates the monthly portion of your annual bill.
Homeowners Insurance: Protects your property against damage. Lenders require this to protect their investment.
HOA Fees: If you buy a condo or a home in a planned community, these fees cover common area maintenance and amenities.
How Interest Rates Affect Affordability
Even a small change in interest rates can significantly impact your monthly payment and the total cost of your loan. For example, on a $300,000 loan, a 1% increase in interest rate can add hundreds of dollars to your monthly payment and tens of thousands to the total interest paid over 30 years.
Strategies to Lower Your Payment
To reduce your monthly burden, consider: increasing your down payment to lower the principal, improving your credit score to qualify for better rates, or opting for a longer loan term (though this increases total interest paid).
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);
var homeInsuranceAnnual = parseFloat(document.getElementById('homeInsurance').value);
var hoaFeesMonthly = parseFloat(document.getElementById('hoaFees').value);
// Error Handling
var errorDisplay = document.getElementById('errorDisplay');
var resultsArea = document.getElementById('resultsArea');
if (isNaN(homePrice) || homePrice <= 0) {
errorDisplay.style.display = 'block';
resultsArea.style.display = 'none';
return;
} else {
errorDisplay.style.display = 'none';
}
// Default values for optional fields if empty/NaN
if (isNaN(downPayment)) downPayment = 0;
if (isNaN(propertyTaxAnnual)) propertyTaxAnnual = 0;
if (isNaN(homeInsuranceAnnual)) homeInsuranceAnnual = 0;
if (isNaN(hoaFeesMonthly)) hoaFeesMonthly = 0;
if (isNaN(interestRateAnnual)) interestRateAnnual = 0;
// Core Calculation Logic
var loanAmount = homePrice – downPayment;
// Prevent negative loan amount
if (loanAmount < 0) loanAmount = 0;
var monthlyRate = (interestRateAnnual / 100) / 12;
var numberOfPayments = loanTermYears * 12;
var monthlyPrincipalInterest = 0;
// Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
if (interestRateAnnual === 0) {
monthlyPrincipalInterest = loanAmount / numberOfPayments;
} else {
monthlyPrincipalInterest = loanAmount *
(monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) /
(Math.pow(1 + monthlyRate, numberOfPayments) – 1);
}
// Other Monthly Costs
var monthlyTax = propertyTaxAnnual / 12;
var monthlyInsurance = homeInsuranceAnnual / 12;
var totalMonthlyPayment = monthlyPrincipalInterest + monthlyTax + monthlyInsurance + hoaFeesMonthly;
// Total Costs
var totalPaymentOverTerm = (monthlyPrincipalInterest * numberOfPayments);
var totalInterestPaid = totalPaymentOverTerm – loanAmount;
var totalCostOfLoan = totalPaymentOverTerm + (monthlyTax * numberOfPayments) + (monthlyInsurance * numberOfPayments) + (hoaFeesMonthly * numberOfPayments);
// Formatting Helpers
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
// Display Results
document.getElementById('resLoanAmount').innerText = formatter.format(loanAmount);
document.getElementById('resPrincipalInterest').innerText = formatter.format(monthlyPrincipalInterest);
document.getElementById('resTax').innerText = formatter.format(monthlyTax);
document.getElementById('resIns').innerText = formatter.format(monthlyInsurance);
document.getElementById('resHOA').innerText = formatter.format(hoaFeesMonthly);
document.getElementById('resTotalMonthly').innerText = formatter.format(totalMonthlyPayment);
document.getElementById('resTotalInterest').innerText = formatter.format(totalInterestPaid);
document.getElementById('resTotalCost').innerText = formatter.format(totalCostOfLoan);
// Show Results
resultsArea.style.display = 'block';
}