Calculating your monthly mortgage payment is crucial for budgeting and understanding the true cost of homeownership. This calculator helps estimate your principal and interest payment based on three key factors: the loan amount, the interest rate, and the loan term.
How the Calculation Works
The standard formula used for calculating a fixed-rate mortgage payment is as follows:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
M = Your total monthly mortgage payment (principal and interest)
P = The principal loan amount (the amount you borrow)
i = Your monthly interest rate. This is your annual interest rate divided by 12. For example, an annual rate of 6.5% becomes 0.065 / 12 = 0.00541667.
n = The total number of payments over the loan's lifetime. This is your loan term in years multiplied by 12. For a 30-year loan, n = 30 * 12 = 360.
Key Factors Influencing Your Mortgage Payment:
Loan Amount (Principal): The larger the amount you borrow, the higher your monthly payments will be.
Interest Rate: This is arguably the most significant factor. Even a small difference in the annual interest rate can lead to thousands of dollars more or less paid over the life of the loan. Higher rates mean higher monthly payments.
Loan Term: A longer loan term (e.g., 30 years vs. 15 years) will result in lower monthly payments because the principal is spread out over more payments. However, you will pay significantly more in interest over the life of the loan.
Important Considerations:
This calculator provides an estimate for the principal and interest (P&I) portion of your mortgage payment only. Your actual total monthly housing expense will likely be higher and include:
Property Taxes: Paid to your local government.
Homeowner's Insurance: Required by lenders to protect against damage.
Private Mortgage Insurance (PMI): Typically required if your down payment is less than 20% for conventional loans.
Homeowner Association (HOA) Dues: If you live in a community with an HOA.
Mortgage rates fluctuate daily based on market conditions, your credit score, down payment, loan type, and other factors. It's always recommended to get pre-approved by a lender to understand the specific rates and terms you qualify for.
function calculateMortgage() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("interestRate").value);
var loanTermYears = parseInt(document.getElementById("loanTerm").value);
var resultDisplay = document.getElementById("result").querySelector("span");
if (isNaN(loanAmount) || isNaN(annualInterestRate) || isNaN(loanTermYears) || loanAmount <= 0 || annualInterestRate < 0 || loanTermYears 0) {
monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
} else {
// If interest rate is 0, payment is just the principal divided by the number of payments
monthlyPayment = loanAmount / numberOfPayments;
}
resultDisplay.textContent = "$" + monthlyPayment.toFixed(2);
resultDisplay.style.color = "#28a745"; // Green for success
}