Please enter valid positive numbers for all fields.
Estimated Monthly Payment$0.00
Loan Principal Amount:$0.00
Total Interest Paid:$0.00
Total Cost of Loan:$0.00
Payoff Date:–
Understanding Your Mortgage Calculation
Navigating the home buying process requires a clear understanding of your financial commitments. Our Mortgage Calculator helps you estimate your monthly payments based on the home price, your down payment, the loan term, and current interest rates. By tweaking these variables, you can determine a budget that fits your lifestyle without overextending your finances.
How the Mortgage Formula Works
A standard fixed-rate mortgage is calculated using an amortization formula. This ensures that your monthly payment remains constant throughout the life of the loan, although the portion allocated to principal and interest changes over time. In the early years, the majority of your payment goes toward interest, while in later years, you pay down more of the principal.
The core components of the calculation are:
Principal (P): The total amount of money borrowed (Home Price minus Down Payment).
Interest Rate (r): The annual percentage rate charged by the lender, divided by 12 to get the monthly rate.
Number of Payments (n): The total number of months in the loan term (e.g., 30 years × 12 months = 360 payments).
Factors That Impact Your Monthly Payment
Even small changes in your mortgage terms can significantly affect your monthly obligation and the total interest paid over the life of the loan:
Down Payment: Putting more money down reduces the principal loan amount, which lowers your monthly payment and saves you money on interest. A down payment of 20% or more typically avoids Private Mortgage Insurance (PMI).
Loan Term: A shorter term (e.g., 15 years vs. 30 years) usually comes with a lower interest rate and significantly less total interest paid, but necessitates a higher monthly payment.
Interest Rate: Your credit score, debt-to-income ratio, and economic conditions influence the rate you are offered. Lowering your rate by even 0.5% can save tens of thousands of dollars over 30 years.
Why Use a Mortgage Calculator?
Before you start house hunting, it is crucial to distinguish between what a bank says you can afford and what you are comfortable paying. This tool allows you to simulate different scenarios, such as "What if interest rates rise to 7%?" or "How much do I save if I put down an extra $10,000?" empowering you to make informed financial decisions.
function calculateMortgage() {
// Get input elements
var priceInput = document.getElementById("homePrice");
var downPaymentInput = document.getElementById("downPayment");
var termInput = document.getElementById("loanTerm");
var rateInput = document.getElementById("interestRate");
var errorDiv = document.getElementById("errorMsg");
var resultsDiv = document.getElementById("resultsArea");
// Get values
var price = parseFloat(priceInput.value);
var downPayment = parseFloat(downPaymentInput.value);
var years = parseFloat(termInput.value);
var annualRate = parseFloat(rateInput.value);
// Validation
if (isNaN(price) || isNaN(downPayment) || isNaN(years) || isNaN(annualRate) ||
price < 0 || downPayment < 0 || years <= 0 || annualRate = price
if (principal <= 0) {
document.getElementById("monthlyPaymentResult").innerHTML = "$0.00";
document.getElementById("principalResult").innerHTML = "$0.00";
document.getElementById("totalInterestResult").innerHTML = "$0.00";
document.getElementById("totalCostResult").innerHTML = formatCurrency(downPayment);
document.getElementById("payoffDateResult").innerHTML = "N/A";
resultsDiv.style.display = "block";
return;
}
var monthlyRate = annualRate / 100 / 12;
var numberOfPayments = years * 12;
var monthlyPayment = 0;
if (annualRate === 0) {
monthlyPayment = principal / numberOfPayments;
} else {
// Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
monthlyPayment = (principal * monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
}
var totalPayment = monthlyPayment * numberOfPayments;
var totalInterest = totalPayment – principal;
// Calculate Payoff Date
var today = new Date();
today.setMonth(today.getMonth() + numberOfPayments);
var options = { year: 'numeric', month: 'long' };
var payoffDate = today.toLocaleDateString("en-US", options);
// Update DOM
document.getElementById("monthlyPaymentResult").innerHTML = formatCurrency(monthlyPayment);
document.getElementById("principalResult").innerHTML = formatCurrency(principal);
document.getElementById("totalInterestResult").innerHTML = formatCurrency(totalInterest);
document.getElementById("totalCostResult").innerHTML = formatCurrency(totalPayment + downPayment); // Total cost includes down payment
document.getElementById("payoffDateResult").innerHTML = payoffDate;
resultsDiv.style.display = "block";
}
function formatCurrency(num) {
return "$" + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}