Please enter valid positive numbers for all fields.
Total Monthly Payment$0.00
Principal & Interest:$0.00
Property Tax (Monthly):$0.00
Home Insurance (Monthly):$0.00
HOA Fees:$0.00
Total Loan Amount:$0.00
Total Interest Paid:$0.00
Total Cost of Loan:$0.00
function calculateMortgage() {
// Get Inputs
var price = parseFloat(document.getElementById('mc_home_price').value);
var down = parseFloat(document.getElementById('mc_down_payment').value);
var rate = parseFloat(document.getElementById('mc_interest_rate').value);
var years = parseFloat(document.getElementById('mc_loan_term').value);
var taxYearly = parseFloat(document.getElementById('mc_property_tax').value);
var insYearly = parseFloat(document.getElementById('mc_home_insurance').value);
var hoaMonthly = parseFloat(document.getElementById('mc_hoa_fees').value);
// Validation
var errorBox = document.getElementById('mc_error');
if (isNaN(price) || isNaN(down) || isNaN(rate) || isNaN(years) || isNaN(taxYearly) || isNaN(insYearly) || isNaN(hoaMonthly) ||
price < 0 || down < 0 || rate < 0 || years = price
if (principal <= 0) {
principal = 0;
// Just display taxes and fees
var totalMonthlyNoLoan = (taxYearly / 12) + (insYearly / 12) + hoaMonthly;
document.getElementById('mc_total_monthly').innerHTML = formatCurrency(totalMonthlyNoLoan);
document.getElementById('mc_pi_monthly').innerHTML = "$0.00";
document.getElementById('mc_tax_monthly').innerHTML = formatCurrency(taxYearly / 12);
document.getElementById('mc_ins_monthly').innerHTML = formatCurrency(insYearly / 12);
document.getElementById('mc_hoa_monthly').innerHTML = formatCurrency(hoaMonthly);
document.getElementById('mc_loan_amount').innerHTML = "$0.00";
document.getElementById('mc_total_interest').innerHTML = "$0.00";
document.getElementById('mc_total_cost').innerHTML = formatCurrency(price);
document.getElementById('mc_result_box').style.display = 'block';
return;
}
var monthlyRate = rate / 100 / 12;
var numberOfPayments = years * 12;
// Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var monthlyPI = 0;
if (rate === 0) {
monthlyPI = principal / numberOfPayments;
} else {
monthlyPI = principal * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
}
var monthlyTax = taxYearly / 12;
var monthlyIns = insYearly / 12;
var totalMonthly = monthlyPI + monthlyTax + monthlyIns + hoaMonthly;
var totalPaidToBank = monthlyPI * numberOfPayments;
var totalInterest = totalPaidToBank – principal;
// Update DOM
document.getElementById('mc_pi_monthly').innerHTML = formatCurrency(monthlyPI);
document.getElementById('mc_tax_monthly').innerHTML = formatCurrency(monthlyTax);
document.getElementById('mc_ins_monthly').innerHTML = formatCurrency(monthlyIns);
document.getElementById('mc_hoa_monthly').innerHTML = formatCurrency(hoaMonthly);
document.getElementById('mc_total_monthly').innerHTML = formatCurrency(totalMonthly);
document.getElementById('mc_loan_amount').innerHTML = formatCurrency(principal);
document.getElementById('mc_total_interest').innerHTML = formatCurrency(totalInterest);
document.getElementById('mc_total_cost').innerHTML = formatCurrency(totalPaidToBank + down); // Total cost of house (excluding ongoing tax/ins)
document.getElementById('mc_result_box').style.display = 'block';
}
function formatCurrency(num) {
return '$' + num.toLocaleString('en-US', { minimumFractionDigits: 2, maximumFractionDigits: 2 });
}
Understanding Your Mortgage Calculation
Calculating your monthly mortgage payment involves more than just paying back the loan amount. To get an accurate picture of your housing budget, you must consider the "PITI" components: Principal, Interest, Taxes, and Insurance.
1. Principal & Interest (P&I)
This is the core of your mortgage payment. The Principal is the money you borrowed to buy the home (Home Price minus Down Payment). The Interest is the fee the lender charges you for borrowing that money. Early in your loan term, a large portion of this payment goes toward interest, while later payments focus more on reducing the principal.
2. Property Taxes
Local governments collect property taxes to fund schools, police, and infrastructure. These are usually assessed annually but are often broken down into monthly installments included in your mortgage payment. Our calculator estimates the monthly impact of an annual tax bill.
3. Homeowners Insurance
Lenders require you to carry insurance to protect the property against damage (fire, theft, storms). Like taxes, the annual premium is typically divided by 12 and added to your monthly bill into an escrow account.
4. HOA Fees
If you buy a condo or a home in a planned community, you may owe Homeowners Association (HOA) dues. While these are rarely paid to the mortgage lender, they are a mandatory monthly cost that affects your ability to pay the loan. Lenders factor this into your Debt-to-Income (DTI) ratio during approval.
How Interest Rates Affect Affordability
Even a small change in interest rates can drastically alter your monthly payment and the total cost of the loan. For example, on a $300,000 loan, the difference between a 6.0% and a 7.0% interest rate can add nearly $200 to your monthly payment and over $70,000 in total interest paid over 30 years.
Tips to Lower Your Monthly Payment
Increase your Down Payment: Paying more upfront reduces the principal loan amount and may eliminate the need for Private Mortgage Insurance (PMI).
Improve your Credit Score: Higher credit scores often qualify for lower interest rates.
Shop for Lower Insurance: compare quotes from different insurance providers to reduce your annual premium.
Consider a Longer Term: While a 30-year term has higher total interest than a 15-year term, the monthly payments are significantly lower.