function calculateMortgage() {
var homePrice = parseFloat(document.getElementById('homePrice').value);
var downPayment = parseFloat(document.getElementById('downPayment').value);
var interestRate = parseFloat(document.getElementById('interestRate').value);
var loanTerm = parseInt(document.getElementById('loanTerm').value);
var propertyTax = parseFloat(document.getElementById('propertyTax').value);
var homeInsurance = parseFloat(document.getElementById('homeInsurance').value);
// Validation
if (isNaN(homePrice) || homePrice <= 0) {
alert("Please enter a valid Home Price.");
return;
}
if (isNaN(downPayment) || downPayment < 0) {
downPayment = 0;
}
if (isNaN(interestRate) || interestRate < 0) {
alert("Please enter a valid Interest Rate.");
return;
}
if (isNaN(propertyTax)) propertyTax = 0;
if (isNaN(homeInsurance)) homeInsurance = 0;
var loanAmount = homePrice – downPayment;
if (loanAmount <= 0) {
alert("Down payment cannot be greater than or equal to Home Price.");
return;
}
var monthlyInterestRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
var monthlyPI = 0;
// Calculate P&I
if (interestRate === 0) {
monthlyPI = loanAmount / numberOfPayments;
} else {
monthlyPI = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
}
// Calculate Escrow (Tax + Insurance) monthly
var monthlyTax = propertyTax / 12;
var monthlyInsurance = homeInsurance / 12;
var monthlyEscrow = monthlyTax + monthlyInsurance;
var totalMonthlyPayment = monthlyPI + monthlyEscrow;
var totalPaymentOverTerm = monthlyPI * numberOfPayments;
var totalInterest = totalPaymentOverTerm – loanAmount;
// Calculate Payoff Date
var today = new Date();
var payoffYear = today.getFullYear() + loanTerm;
var payoffMonth = today.toLocaleString('default', { month: 'long' });
var payoffDateString = payoffMonth + " " + payoffYear;
// Update DOM
document.getElementById('resPI').innerText = "$" + monthlyPI.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resEscrow').innerText = "$" + monthlyEscrow.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resTotal').innerText = "$" + totalMonthlyPayment.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resLoanAmount').innerText = "$" + loanAmount.toLocaleString('en-US', {minimumFractionDigits: 0, maximumFractionDigits: 0});
document.getElementById('resTotalInterest').innerText = "$" + totalInterest.toLocaleString('en-US', {minimumFractionDigits: 0, maximumFractionDigits: 0});
document.getElementById('resPayoffDate').innerText = payoffDateString;
document.getElementById('results').style.display = 'block';
}
How to Use This Mortgage Payment Calculator
Purchasing a home is one of the largest financial decisions you will make. Our comprehensive Mortgage Calculator helps you estimate your monthly payments accurately by factoring in not just the principal and interest, but also property taxes and homeowners insurance (PITI). Simply enter your home price, down payment, expected interest rate, and loan term to get an instant breakdown.
Understanding Your Mortgage Breakdown
When you take out a mortgage, your monthly payment is typically composed of four distinct parts, often referred to as PITI:
Principal: The portion of your payment that reduces the loan balance. In the early years of your loan, this amount is small but grows over time.
Interest: The fee charged by the lender for borrowing the money. This makes up the majority of your payment at the beginning of the loan term.
Taxes: Property taxes assessed by your local government. These are usually held in an escrow account by your lender and paid annually on your behalf.
Insurance: Homeowners insurance protects your property against damage. Like taxes, this is often bundled into your monthly payment via escrow.
Why Your Interest Rate Matters
Even a small difference in your interest rate can have a massive impact on your total cost. For example, on a $300,000 loan, the difference between a 6% and a 7% interest rate can cost you tens of thousands of dollars over the life of a 30-year loan. Use this calculator to test different rate scenarios to see how refinancing or improving your credit score could save you money.
Tips for Lowering Your Monthly Payment
If the estimated payment is higher than your budget allows, consider these strategies:
Increase Your Down Payment: Putting more money down reduces the principal loan amount, which lowers both your monthly payment and total interest paid.
Extend the Loan Term: Opting for a 30-year term instead of a 15-year term will lower your monthly obligation, though you will pay more in interest over the long run.
Shop for Lower Insurance: Homeowners insurance rates vary significantly by provider. Shopping around can shave money off your monthly escrow costs.
Eliminate PMI: If you put down less than 20%, you may have to pay Private Mortgage Insurance (PMI). Saving for a 20% down payment removes this extra cost.
Frequently Asked Questions
What is an escrow account?
An escrow account is a savings account managed by your mortgage servicer. A portion of your monthly payment goes into this account to pay for property taxes and insurance premiums when they are due.
How much house can I afford?
A general rule of thumb is that your total housing costs (Principal, Interest, Taxes, Insurance) should not exceed 28% of your gross monthly income. Use the "Total Monthly Payment" result from this calculator to compare against your income.