Calculating your potential monthly mortgage payment is a crucial first step in the home buying process. This Mortgage Payment Calculator helps you estimate your monthly housing costs by factoring in not just the loan principal and interest, but also property taxes, homeowners insurance, and HOA fees.
How the Calculation Works
Your total monthly payment is typically composed of four main parts, often referred to as PITI (Principal, Interest, Taxes, and Insurance):
Principal: The portion of your payment that goes toward paying down the loan balance (the home price minus your down payment).
Interest: The cost of borrowing money from your lender. Higher interest rates significantly increase your monthly payment and the total cost of the loan.
Property Taxes: Taxes assessed by your local government, usually held in an escrow account by your lender and paid annually.
Homeowners Insurance: Protection for your property against damage, also typically paid through escrow.
If you purchase a condo or a home in a planned community, you may also have HOA (Homeowners Association) Fees, which are paid separately but impact your monthly affordability.
Factors That Affect Your Payment
Several variables can drastically change your monthly financial obligation:
Down Payment: Putting more money down reduces your loan amount, which lowers your monthly principal and interest payment. A down payment of 20% or more typically avoids Private Mortgage Insurance (PMI).
Loan Term: A 30-year term offers lower monthly payments but results in more interest paid over the life of the loan compared to a 15-year term.
Interest Rate: Even a small difference in rate (e.g., 0.5%) can save or cost you tens of thousands of dollars over the life of the mortgage.
Why Use a Mortgage Calculator?
Before applying for a loan, it is essential to determine a budget that fits your lifestyle. Lenders may qualify you for a higher amount than you are comfortable paying. By using this calculator, you can adjust the home price, down payment, and interest rate to see different scenarios and find a monthly payment that aligns with your financial goals.
function calculateMortgage() {
// 1. Get references to DOM elements
var elHomePrice = document.getElementById('homePrice');
var elDownPayment = document.getElementById('downPayment');
var elInterestRate = document.getElementById('interestRate');
var elLoanTerm = document.getElementById('loanTerm');
var elPropertyTax = document.getElementById('propertyTax');
var elHomeInsurance = document.getElementById('homeInsurance');
var elHoaFees = document.getElementById('hoaFees');
var elResultsBox = document.getElementById('resultsBox');
var elErrorMsg = document.getElementById('errorMsg');
// 2. Parse values
var homePrice = parseFloat(elHomePrice.value);
var downPayment = parseFloat(elDownPayment.value);
var interestRate = parseFloat(elInterestRate.value);
var loanTermYears = parseInt(elLoanTerm.value);
var propertyTaxYearly = parseFloat(elPropertyTax.value);
var homeInsuranceYearly = parseFloat(elHomeInsurance.value);
var hoaFeesMonthly = parseFloat(elHoaFees.value);
// 3. Validation
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTermYears) ||
homePrice < 0 || downPayment < 0 || interestRate = home price
if (loanAmount 0) {
if (monthlyRate === 0) {
monthlyPI = loanAmount / totalPayments;
} else {
// M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
monthlyPI = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, totalPayments)) / (Math.pow(1 + monthlyRate, totalPayments) – 1);
}
}
// Other Monthly Costs
var monthlyTax = propertyTaxYearly / 12;
var monthlyInsurance = homeInsuranceYearly / 12;
// Ensure HOA is a number (default to 0 if empty/NaN handled above but just in case)
if (isNaN(hoaFeesMonthly)) hoaFeesMonthly = 0;
// Total Monthly Payment
var totalMonthlyPayment = monthlyPI + monthlyTax + monthlyInsurance + hoaFeesMonthly;
// Total Interest Paid
var totalCostOfLoan = (monthlyPI * totalPayments);
var totalInterest = totalCostOfLoan – loanAmount;
if (totalInterest < 0) totalInterest = 0;
// 5. Update UI
// Helper format function
function formatMoney(num) {
return '$' + num.toLocaleString('en-US', { minimumFractionDigits: 2, maximumFractionDigits: 2 });
}
document.getElementById('resPI').innerText = formatMoney(monthlyPI);
document.getElementById('resTax').innerText = formatMoney(monthlyTax);
document.getElementById('resIns').innerText = formatMoney(monthlyInsurance);
document.getElementById('resHOA').innerText = formatMoney(hoaFeesMonthly);
document.getElementById('resTotal').innerText = formatMoney(totalMonthlyPayment);
document.getElementById('resLoanAmount').innerText = formatMoney(loanAmount);
document.getElementById('resTotalInterest').innerText = formatMoney(totalInterest);
// Show results
elResultsBox.style.display = 'block';
}