Please enter valid numeric values for Home Price, Rate, and Term.
Estimated Monthly Payment$0.00
Principal & Interest$0.00
Property Tax (Monthly)$0.00
Home Insurance (Monthly)$0.00
HOA Fees (Monthly)$0.00
Total Loan Amount$0.00
Total Interest Paid (Over Life of Loan)$0.00
Total Cost of Mortgage$0.00
function calculateMortgage() {
// 1. Get Elements
var priceInput = document.getElementById("hmc-price");
var downInput = document.getElementById("hmc-down");
var rateInput = document.getElementById("hmc-rate");
var termInput = document.getElementById("hmc-term");
var taxInput = document.getElementById("hmc-tax");
var insInput = document.getElementById("hmc-insurance");
var hoaInput = document.getElementById("hmc-hoa");
var errorBox = document.getElementById("hmc-error");
var resultBox = document.getElementById("hmc-results");
// 2. Parse Values
var price = parseFloat(priceInput.value);
var down = parseFloat(downInput.value) || 0;
var rate = parseFloat(rateInput.value);
var term = parseFloat(termInput.value);
var annualTax = parseFloat(taxInput.value) || 0;
var annualIns = parseFloat(insInput.value) || 0;
var monthlyHoa = parseFloat(hoaInput.value) || 0;
// 3. Validation
if (isNaN(price) || isNaN(rate) || isNaN(term) || price <= 0 || term <= 0) {
errorBox.style.display = "block";
resultBox.style.display = "none";
return;
}
errorBox.style.display = "none";
// 4. Calculations
var loanAmount = price – down;
// Check if down payment is greater than home price
if (loanAmount 0 && rate > 0) {
monthlyPI = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
} else if (loanAmount > 0 && rate === 0) {
monthlyPI = loanAmount / numberOfPayments;
}
// Other monthly costs
var monthlyTax = annualTax / 12;
var monthlyIns = annualIns / 12;
var totalMonthlyPayment = monthlyPI + monthlyTax + monthlyIns + monthlyHoa;
// Totals over life of loan
var totalPaidToBank = monthlyPI * numberOfPayments;
var totalInterest = totalPaidToBank – loanAmount;
var totalCostOfMortgage = totalPaidToBank + (monthlyTax * numberOfPayments) + (monthlyIns * numberOfPayments) + (monthlyHoa * numberOfPayments);
// 5. Display Results
document.getElementById("hmc-res-total-monthly").innerHTML = "$" + totalMonthlyPayment.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("hmc-res-pi").innerHTML = "$" + monthlyPI.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("hmc-res-tax").innerHTML = "$" + monthlyTax.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("hmc-res-ins").innerHTML = "$" + monthlyIns.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("hmc-res-hoa").innerHTML = "$" + monthlyHoa.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("hmc-res-loan-amount").innerHTML = "$" + loanAmount.toLocaleString('en-US', {minimumFractionDigits: 0, maximumFractionDigits: 0});
document.getElementById("hmc-res-total-interest").innerHTML = "$" + totalInterest.toLocaleString('en-US', {minimumFractionDigits: 0, maximumFractionDigits: 0});
document.getElementById("hmc-res-total-cost").innerHTML = "$" + totalCostOfMortgage.toLocaleString('en-US', {minimumFractionDigits: 0, maximumFractionDigits: 0});
resultBox.style.display = "block";
}
Complete Guide to Calculating Your Monthly Mortgage Payment
Purchasing a home is likely the largest financial commitment you will make in your lifetime. Understanding exactly how much that home will cost you on a monthly basis—and over the life of the loan—is crucial for financial stability. This Mortgage Calculator goes beyond simple principal and interest to include critical factors like property taxes, homeowner's insurance, and HOA fees.
How the Mortgage Formula Works
Most mortgages use an amortization formula to determine your monthly payments. While the math can be complex, the concept is straightforward: you are paying back a portion of the borrowed money (Principal) plus the cost of borrowing that money (Interest).
The standard formula used in this calculator 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 = Total number of months (Loan years multiplied by 12)
Understanding the Input Factors
To get the most accurate result from the calculator above, it helps to understand what each field represents:
1. Home Price & Down Payment
The Home Price is the agreed-upon sale price of the property. The Down Payment is the cash you pay upfront. The difference between these two figures is your Loan Amount. A higher down payment reduces your monthly principal and interest payment and reduces the total interest paid over the life of the loan. Generally, a down payment of 20% or more allows you to avoid Private Mortgage Insurance (PMI).
2. Interest Rate
Your interest rate is determined by the broader economic market and your personal credit score. Even a small difference in rate (e.g., 6.0% vs 6.5%) can result in tens of thousands of dollars in savings or extra costs over a 30-year term. It is always recommended to shop around with multiple lenders.
3. Loan Term
The Loan Term is the duration of the mortgage. The most common terms in the United States are:
30 Years: Lower monthly payments, but you pay significantly more in interest over time.
15 Years: Higher monthly payments, but you build equity faster and pay much less interest.
The "Hidden" Costs: Taxes, Insurance, and HOAs
Many first-time homebuyers focus solely on the mortgage payment and forget about the PITI (Principal, Interest, Taxes, Insurance) calculation. This calculator allows you to input:
Property Tax: Paid to your local government to fund services like schools and roads. This is usually calculated as a percentage of your home's assessed value.
Homeowner's Insurance: Protects your property against damage. Lenders require this coverage.
HOA Fees: If you buy a condo or a home in a planned community, you may owe monthly Homeowners Association dues to cover common area maintenance.
Strategies to Lower Your Monthly Payment
If the result from the calculator is higher than your budget allows, consider these strategies:
Increase your Down Payment: This lowers the loan principal immediately.
Improve your Credit Score: A better score qualifies you for lower interest rates.
Shop for Insurance: Insurance premiums vary wildly; get quotes from multiple providers.
Consider a Longer Term: While it costs more in the long run, extending a 15-year loan to a 30-year loan will drop the monthly obligation.