Please enter valid positive numbers for Home Price, Down Payment, and Interest Rate.
Estimated Monthly Payment
$0.00
Principal & Interest:
Tax & Insurance:
Total Loan Amount:
Total Interest Paid:
Understanding Your Mortgage Payments
Calculating your monthly mortgage payment is the first critical step in the home-buying journey. This Mortgage Payment Calculator helps prospective homeowners estimate their monthly housing costs by factoring in the principal loan amount, interest rates, taxes, and insurance. By adjusting the home price and down payment, you can determine a budget that fits your financial goals.
How the Mortgage Formula Works
Most fixed-rate mortgages use a standard amortization formula to determine monthly payments. The calculation ensures that the loan is paid off completely by the end of the term. The core formula used in this tool is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
M = Total monthly payment
P = Principal loan amount (Home Price minus Down Payment)
i = Monthly interest rate (Annual rate divided by 12)
n = Number of months (Loan term in years multiplied by 12)
Factors Affecting Your Monthly Payment
While the formula covers the loan itself, your actual monthly check often includes other costs known as PITI (Principal, Interest, Taxes, and Insurance):
Principal: The portion of money that goes towards paying down the balance of the loan.
Interest: The cost of borrowing money from the lender. Higher credit scores can help secure lower rates.
Property Taxes: Taxes paid to your local government, usually held in an escrow account by the lender.
Homeowners Insurance: Protection against damage to your property, which is required by lenders.
Why Use a Mortgage Calculator?
Using a calculator allows you to stress-test your budget. For example, a small increase in interest rates from 6% to 7% can significantly increase your monthly obligation. Additionally, seeing the "Total Interest Paid" over the life of a 30-year loan can motivate buyers to make a larger down payment or choose a 15-year term to save tens of thousands of dollars.
function calculateMortgage() {
// 1. Get Input Values
var homePrice = parseFloat(document.getElementById('mpcHomePrice').value);
var downPayment = parseFloat(document.getElementById('mpcDownPayment').value);
var interestRate = parseFloat(document.getElementById('mpcInterestRate').value);
var termYears = parseInt(document.getElementById('mpcLoanTerm').value);
var taxYearly = parseFloat(document.getElementById('mpcPropertyTax').value);
var insuranceYearly = parseFloat(document.getElementById('mpcInsurance').value);
// 2. Validation
var errorDiv = document.getElementById('mpcErrorMessage');
var resultDiv = document.getElementById('mpcResult');
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(interestRate) || homePrice <= 0 || interestRate < 0) {
errorDiv.style.display = 'block';
resultDiv.style.display = 'none';
return;
} else {
errorDiv.style.display = 'none';
}
// Handle optional inputs if empty
if (isNaN(taxYearly)) taxYearly = 0;
if (isNaN(insuranceYearly)) insuranceYearly = 0;
// 3. Core Calculation Logic
var principal = homePrice – downPayment;
// Check if downpayment is larger than price
if (principal < 0) {
alert("Down payment cannot be greater than home price.");
return;
}
var monthlyInterestRate = (interestRate / 100) / 12;
var numberOfPayments = termYears * 12;
var monthlyPI = 0;
// Edge case: 0% interest
if (interestRate === 0) {
monthlyPI = principal / numberOfPayments;
} else {
var x = Math.pow(1 + monthlyInterestRate, numberOfPayments);
monthlyPI = (principal * x * monthlyInterestRate) / (x – 1);
}
var monthlyTax = taxYearly / 12;
var monthlyInsurance = insuranceYearly / 12;
var totalMonthly = monthlyPI + monthlyTax + monthlyInsurance;
var totalInterest = (monthlyPI * numberOfPayments) – principal;
// 4. Update UI
document.getElementById('mpcTotalMonthly').innerText = "$" + totalMonthly.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('mpcPI').innerText = "$" + monthlyPI.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('mpcEscrow').innerText = "$" + (monthlyTax + monthlyInsurance).toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('mpcLoanAmount').innerText = "$" + principal.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 0});
document.getElementById('mpcTotalInterest').innerText = "$" + totalInterest.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 0});
// Show result
resultDiv.style.display = 'block';
}