Your estimated monthly principal and interest payment will be: $0.00
Understanding Your Mortgage Payment
A mortgage is a long-term loan used to purchase real estate, where the property itself serves as collateral. The monthly mortgage payment is a critical figure for any homebuyer, and it's typically composed of several components, the most fundamental being principal and interest. This calculator focuses on estimating that core principal and interest (P&I) payment.
The Math Behind the Mortgage Payment
The calculation for a fixed-rate mortgage's monthly principal and interest payment is based on the following formula:
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 calculated by dividing your annual interest rate by 12. For example, if your annual rate is 4.5%, your monthly rate (i) is 0.045 / 12 = 0.00375.
n = The total number of payments over the loan's lifetime. This is calculated by multiplying the loan term in years by 12. For a 30-year mortgage, n = 30 * 12 = 360 payments.
How to Use This Calculator:
Loan Amount: Enter the total amount you intend to borrow for the property.
Annual Interest Rate: Input the yearly interest rate offered by your lender. This is typically a percentage.
Loan Term: Select the duration of your mortgage in years from the dropdown menu. Common terms include 15, 20, 25, and 30 years.
Clicking "Calculate Monthly Payment" will provide an estimate of the principal and interest portion of your monthly payment.
Important Considerations:
This calculator provides an estimate of the Principal and Interest (P&I) payment only. Your actual total monthly housing expense will likely be higher and may include:
Property Taxes: Annual taxes assessed by your local government.
Homeowner's Insurance: Coverage for damage or loss to your home.
Private Mortgage Insurance (PMI): If your down payment is less than 20% of the home's value, lenders often require PMI.
HOA Fees: If applicable, for homeowners association dues.
These additional costs are often bundled into your monthly payment by lenders through an escrow account. Always consult with your mortgage lender for a precise breakdown of all costs associated with your specific loan.
function calculateMortgage() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var loanTerm = parseInt(document.getElementById("loanTerm").value);
var resultElement = document.getElementById("result").querySelector("span");
if (isNaN(loanAmount) || isNaN(annualInterestRate) || isNaN(loanTerm) || loanAmount <= 0 || annualInterestRate < 0 || loanTerm 0) {
monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
} else {
// Handle case of 0% interest rate
monthlyPayment = loanAmount / numberOfPayments;
}
var formattedMonthlyPayment = "$" + monthlyPayment.toFixed(2);
resultElement.textContent = formattedMonthlyPayment;
resultElement.style.color = "#28a745"; // Green for success
}