30 Years Fixed
20 Years Fixed
15 Years Fixed
10 Years Fixed
Estimated Monthly Payment
$0.00
Total Principal: $0.00
Total Interest Paid: $0.00
Total Cost of Loan: $0.00
function calculateMortgage() {
var homePrice = parseFloat(document.getElementById("homePrice").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var annualRate = parseFloat(document.getElementById("interestRate").value);
var years = parseInt(document.getElementById("loanTerm").value);
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(annualRate) || homePrice <= 0) {
alert("Please enter valid positive numbers for all fields.");
return;
}
var principal = homePrice – downPayment;
if (principal <= 0) {
alert("Down payment cannot be greater than or equal to the home price.");
return;
}
var monthlyRate = (annualRate / 100) / 12;
var numberOfPayments = years * 12;
var monthlyPayment;
if (monthlyRate === 0) {
monthlyPayment = principal / numberOfPayments;
} else {
monthlyPayment = (principal * monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
}
var totalCost = monthlyPayment * numberOfPayments;
var totalInterest = totalCost – principal;
document.getElementById("monthlyPayment").innerHTML = "$" + monthlyPayment.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalPrincipal").innerHTML = "$" + principal.toLocaleString();
document.getElementById("totalInterest").innerHTML = "$" + totalInterest.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalCost").innerHTML = "$" + totalCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resultArea").style.display = "block";
}
Understanding Your Monthly Mortgage Payment
Buying a home is often the largest financial commitment you will ever make. Using a Mortgage Payment Calculator helps you look beyond the sticker price of a house and understand exactly how much it will cost you on a month-to-month basis. This allows for better budgeting and ensures you don't overextend your finances.
How the Mortgage Calculation Works
The standard formula for calculating a fixed-rate mortgage payment is based on amortization. This means your monthly payment stays the same for the duration of the loan, but the proportion of the payment going toward the principal (the actual loan balance) versus the interest changes over time.
The math follows this standard formula: 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 months).
n: Number of months (Years of the loan multiplied by 12).
Key Factors Impacting Your Payment
Down Payment: The more money you put down upfront, the lower your principal loan amount will be. This directly reduces your monthly payment and the total interest you will pay over the life of the loan.
Interest Rate: Even a small difference of 0.5% in your interest rate can result in tens of thousands of dollars in savings (or extra costs) over 30 years.
Loan Term: A 15-year mortgage will have higher monthly payments than a 30-year mortgage, but you will pay significantly less interest overall and own your home twice as fast.
Real-World Example
Let's say you purchase a home for $400,000 with a 20% down payment ($80,000). You secure a 30-year fixed mortgage at an interest rate of 6.5%.
Principal Loan Amount: $320,000
Monthly Payment (Principal + Interest): $2,022.62
Total Interest Paid: $408,143.20
Total Cost of Loan: $728,143.20
As seen in this example, the interest paid over 30 years actually exceeds the original loan amount. This highlights why it is vital to shop for the best interest rates and consider making extra principal payments when possible.
What is Not Included?
Please note that this calculator focuses on Principal and Interest (P&I). In a real-world scenario, your monthly housing expense may also include:
Property Taxes: Levied by your local government.
Homeowners Insurance: Required by lenders to protect the asset.
Private Mortgage Insurance (PMI): Usually required if your down payment is less than 20%.
HOA Fees: If the property is part of a homeowners association.