Please enter valid positive numbers for Home Price, Interest Rate, and Term.
Estimated Monthly Payment
$0.00
Principal & Interest
$0.00
Property Tax
$0.00
Home Insurance
$0.00
HOA Fees
$0.00
Loan Details: Amount Financed: $0 | Total Interest: $0
How to Use This Mortgage Payment Calculator
Understanding your monthly mortgage obligation is the first step in the home buying journey. This calculator breaks down the total monthly cost of owning a home, going beyond just the loan repayment to include taxes, insurance, and association fees.
To get the most accurate result, fill in the following fields:
Home Price: The total purchase price of the property.
Down Payment: The cash amount you are paying upfront. The calculator assumes the rest is financed.
Interest Rate: Your expected annual interest rate based on current market conditions and your credit score.
Loan Term: The duration of the loan, typically 15 or 30 years.
Escrow Costs: Include estimates for Property Tax and Homeowners Insurance to see your "PITI" (Principal, Interest, Taxes, Insurance) payment.
Understanding the Amortization Formula
Your monthly principal and interest payment is calculated using the standard amortization formula:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
Where:
M = Total monthly payment
P = Principal loan amount
i = Monthly interest rate (Annual rate / 12)
n = Number of payments (Years × 12)
Factors Affecting Your Monthly Payment
While the loan principal and interest rate are the primary drivers, other factors significantly impact affordability:
Property Taxes and Insurance
Lenders often require you to pay 1/12th of your estimated annual property taxes and homeowners insurance into an escrow account each month. This ensures these bills are paid on time but increases your monthly cash outflow significantly.
HOA Fees
If you are buying a condo or a home in a planned community, Homeowners Association (HOA) fees are usually paid separately from the mortgage but are critical to your monthly budget. Lenders factor these into your debt-to-income ratio.
Down Payment Size
A larger down payment reduces the principal loan amount, thereby lowering your monthly Principal & Interest payment. Additionally, putting down at least 20% often removes the need for Private Mortgage Insurance (PMI), saving you hundreds of dollars monthly.
function calculateMortgage() {
// 1. Get input values by ID strictly
var homePrice = parseFloat(document.getElementById("mcHomePrice").value);
var downPayment = parseFloat(document.getElementById("mcDownPayment").value);
var interestRate = parseFloat(document.getElementById("mcInterestRate").value);
var loanTerm = parseFloat(document.getElementById("mcLoanTerm").value);
var propertyTaxYearly = parseFloat(document.getElementById("mcPropertyTax").value);
var insuranceYearly = parseFloat(document.getElementById("mcInsurance").value);
var hoaMonthly = parseFloat(document.getElementById("mcHOA").value);
// 2. Default values if inputs are empty but allow calculation
if (isNaN(downPayment)) downPayment = 0;
if (isNaN(propertyTaxYearly)) propertyTaxYearly = 0;
if (isNaN(insuranceYearly)) insuranceYearly = 0;
if (isNaN(hoaMonthly)) hoaMonthly = 0;
// 3. Validation checks
var errorDiv = document.getElementById("mcErrorMessage");
var resultDiv = document.getElementById("mcResults");
if (isNaN(homePrice) || homePrice <= 0 || isNaN(interestRate) || isNaN(loanTerm) || loanTerm <= 0) {
errorDiv.style.display = "block";
resultDiv.style.display = "none";
return;
}
errorDiv.style.display = "none";
resultDiv.style.display = "block";
// 4. Core Calculations
var principal = homePrice – downPayment;
// Handle edge case: principal <= 0
if (principal < 0) principal = 0;
var monthlyInterestRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
var monthlyPI = 0;
// Amortization logic
if (interestRate === 0) {
monthlyPI = principal / numberOfPayments;
} else {
var x = Math.pow(1 + monthlyInterestRate, numberOfPayments);
monthlyPI = principal * ((monthlyInterestRate * x) / (x – 1));
}
// Secondary Monthly Costs
var monthlyTax = propertyTaxYearly / 12;
var monthlyIns = insuranceYearly / 12;
var totalMonthlyPayment = monthlyPI + monthlyTax + monthlyIns + hoaMonthly;
// Total Interest & Cost Calculation
var totalCostOfLoan = (monthlyPI * numberOfPayments);
var totalInterest = totalCostOfLoan – principal;
// 5. Formatting Helper
function formatMoney(num) {
return "$" + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
// 6. Update DOM
document.getElementById("mcTotalMonthly").innerHTML = formatMoney(totalMonthlyPayment);
document.getElementById("mcResultPI").innerHTML = formatMoney(monthlyPI);
document.getElementById("mcResultTax").innerHTML = formatMoney(monthlyTax);
document.getElementById("mcResultIns").innerHTML = formatMoney(monthlyIns);
document.getElementById("mcResultHOA").innerHTML = formatMoney(hoaMonthly);
document.getElementById("mcLoanAmount").innerHTML = formatMoney(principal);
document.getElementById("mcTotalInterest").innerHTML = formatMoney(totalInterest);
}