Buying a home is one of the largest financial decisions you will make. While the listing price is important, your monthly mortgage payment is what ultimately determines affordability. This calculator provides a comprehensive breakdown of your PITI (Principal, Interest, Taxes, and Insurance), ensuring you aren't caught off guard by hidden costs.
What Goes Into Your Monthly Payment?
Your monthly housing payment consists of several components:
Principal: The portion of your payment that goes toward paying down the loan balance.
Interest: The cost of borrowing money from the lender. In the early years of a mortgage, a large percentage of your payment goes toward interest.
Property Taxes: Taxes paid to your local government, usually collected by the lender in an escrow account and paid annually.
Homeowners Insurance: Protects your property against damage. Like taxes, this is often divided into monthly installments.
HOA Fees: If you live in a community with a Homeowners Association, these fees are paid separately but impact your total monthly budget.
The Impact of Interest Rates
Even a small difference in interest rates can significantly affect your monthly payment and the total interest paid over the life of the loan. For example, on a $300,000 loan, the difference between a 6% and a 7% interest rate is roughly $200 per month and over $70,000 in total interest over 30 years.
30-Year vs. 15-Year Mortgages
Choosing your loan term is a trade-off between monthly cash flow and long-term savings:
30-Year Fixed: Offers lower monthly payments, making the home more affordable day-to-day, but you will pay significantly more interest over the life of the loan.
15-Year Fixed: Requires higher monthly payments, but you build equity faster and pay far less in total interest.
How to Use This Calculator
Enter the Home Price and your planned Down Payment to determine the loan amount. Input your expected Interest Rate (check current market rates for accuracy). Don't forget to estimate Property Taxes (typically 1-2% of home value annually) and Insurance to get a realistic view of your total monthly obligation.
function calculateMortgage() {
// 1. Get Input Values
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);
// Validation to prevent NaN errors
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm)) {
alert("Please enter valid numbers for Home Price, Down Payment, Rate, and Term.");
return;
}
// Set default values for optional fields if empty/NaN
if (isNaN(propertyTax)) propertyTax = 0;
if (isNaN(homeInsurance)) homeInsurance = 0;
if (isNaN(hoaFees)) hoaFees = 0;
// 2. Perform Calculations
var loanAmount = homePrice – downPayment;
// Handle case where down payment is greater than home price
if (loanAmount < 0) {
loanAmount = 0;
}
var monthlyRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
var monthlyPrincipalInterest = 0;
// Standard Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
if (monthlyRate === 0) {
monthlyPrincipalInterest = loanAmount / numberOfPayments;
} else {
monthlyPrincipalInterest = loanAmount *
(monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) /
(Math.pow(1 + monthlyRate, numberOfPayments) – 1);
}
// Monthly Tax and Insurance
var monthlyTaxVal = propertyTax / 12;
var monthlyInsuranceVal = homeInsurance / 12;
// Total Monthly Payment
var totalMonthly = monthlyPrincipalInterest + monthlyTaxVal + monthlyInsuranceVal + hoaFees;
// Total Interest Paid (Total P&I Payments – Loan Amount)
var totalPaymentOverLife = monthlyPrincipalInterest * numberOfPayments;
var totalInterest = totalPaymentOverLife – loanAmount;
// 3. Display Results
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
document.getElementById('totalMonthlyPayment').innerHTML = formatter.format(totalMonthly);
document.getElementById('principalInterest').innerHTML = formatter.format(monthlyPrincipalInterest);
document.getElementById('monthlyTax').innerHTML = formatter.format(monthlyTaxVal);
document.getElementById('monthlyInsurance').innerHTML = formatter.format(monthlyInsuranceVal);
document.getElementById('monthlyHOA').innerHTML = formatter.format(hoaFees);
document.getElementById('totalLoanAmount').innerHTML = formatter.format(loanAmount);
document.getElementById('totalInterestPaid').innerHTML = formatter.format(totalInterest);
// Show results section
document.getElementById('resultsArea').style.display = 'block';
}