Purchasing a home is one of the most significant financial decisions you will make. Using our Mortgage Calculator allows you to estimate your monthly payments accurately, ensuring you budget effectively for your new property. This tool breaks down the Principal, Interest, Taxes, and Insurance (PITI) to give you a clear picture of your financial commitment.
Key Factors Affecting Your Payment
When calculating your mortgage, several variables impact the final monthly cost:
Home Price & Down Payment: The difference between these two figures determines your Loan Amount. A larger down payment reduces the principal loan amount, thereby lowering your monthly interest payments and potentially eliminating the need for Private Mortgage Insurance (PMI).
Interest Rate: This is the cost of borrowing money, expressed as an annual percentage. Even a fractional difference (e.g., 0.5%) can save or cost you tens of thousands of dollars over the life of a 30-year loan.
Loan Term: Most mortgages are 15 or 30 years. A shorter term means higher monthly payments but significantly less interest paid overall. A longer term offers lower monthly payments but results in higher total interest costs.
What is PITI?
Your monthly mortgage payment is often referred to as PITI, standing for:
Principal: The portion of your payment that pays down the actual balance of the loan.
Interest: The money charged by the lender for the privilege of borrowing the principal.
Taxes: Property taxes collected by your local government, often held in escrow by your lender and paid annually.
Insurance: Homeowners insurance protects your property against damage. Like taxes, this is often divided into monthly installments.
How the Calculation Works
The core of the mortgage calculation uses the standard amortization formula:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
Where M is the monthly payment, P is the principal loan amount, i is the monthly interest rate, and n is the number of months required to repay the loan. Our calculator automatically handles this math while adding your estimated tax and insurance obligations.
function calculateMortgage() {
// 1. Get input values by ID
var homePrice = document.getElementById("homePrice").value;
var downPayment = document.getElementById("downPayment").value;
var interestRate = document.getElementById("interestRate").value;
var loanTerm = document.getElementById("loanTerm").value;
var propertyTax = document.getElementById("propertyTax").value;
var homeInsurance = document.getElementById("homeInsurance").value;
var resultDiv = document.getElementById("results");
var errorDiv = document.getElementById("errorMsg");
// 2. Validate inputs
if (homePrice === "" || downPayment === "" || interestRate === "" || loanTerm === "" || propertyTax === "" || homeInsurance === "") {
errorDiv.style.display = "block";
resultDiv.style.display = "none";
return;
}
// Parse values to floats
var price = parseFloat(homePrice);
var down = parseFloat(downPayment);
var rate = parseFloat(interestRate);
var years = parseFloat(loanTerm);
var tax = parseFloat(propertyTax);
var insurance = parseFloat(homeInsurance);
// Check for negative numbers or non-numeric
if (isNaN(price) || isNaN(down) || isNaN(rate) || isNaN(years) || isNaN(tax) || isNaN(insurance) || price < 0 || years <= 0) {
errorDiv.style.display = "block";
resultDiv.style.display = "none";
return;
}
// Hide error if validation passes
errorDiv.style.display = "none";
// 3. Perform Calculations
var principal = price – down;
// Handle case where down payment is greater than price
if (principal < 0) {
principal = 0;
}
var monthlyInterestRate = (rate / 100) / 12;
var numberOfPayments = years * 12;
var monthlyPrincipalInterest = 0;
// Standard Mortgage Formula
if (rate === 0) {
monthlyPrincipalInterest = principal / numberOfPayments;
} else {
// M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var pow = Math.pow((1 + monthlyInterestRate), numberOfPayments);
monthlyPrincipalInterest = principal * ((monthlyInterestRate * pow) / (pow – 1));
}
// Monthly Tax and Insurance
var monthlyTax = tax / 12;
var monthlyInsurance = insurance / 12;
var totalMonthlyPayment = monthlyPrincipalInterest + monthlyTax + monthlyInsurance;
// 4. Update UI
document.getElementById("totalMonthlyPayment").innerHTML = "$" + totalMonthlyPayment.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("piPayment").innerHTML = "$" + monthlyPrincipalInterest.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("taxPayment").innerHTML = "$" + monthlyTax.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("insPayment").innerHTML = "$" + monthlyInsurance.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalLoanAmount").innerHTML = "$" + principal.toLocaleString('en-US', {minimumFractionDigits: 0, maximumFractionDigits: 0});
// Show results
resultDiv.style.display = "block";
}