Calculate your estimated monthly mortgage payment (principal and interest).
Your Estimated Monthly Payment:
$0.00
Understanding Your Monthly Mortgage Payment
The monthly mortgage payment is the amount you pay each month to your lender. It typically consists of principal and interest (P&I). While this calculator focuses on P&I, a full mortgage payment often includes property taxes, homeowners insurance (often called 'escrow'), and potentially private mortgage insurance (PMI) or HOA fees. These additional costs will increase your total monthly housing expense.
The Calculation Formula
The standard formula used to calculate the monthly mortgage payment (M) is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
M = Your total monthly mortgage payment (Principal & Interest)
P = The principal loan amount (the total amount you borrow)
i = Your monthly interest rate. This is your annual interest rate divided by 12. For example, a 6% annual rate is 0.06 / 12 = 0.005 per month.
n = The total number of payments over the loan's lifetime. This is your loan term in years multiplied by 12. For example, a 30-year mortgage has 30 * 12 = 360 payments.
How to Use This Calculator
To estimate your monthly mortgage payment, follow these steps:
Loan Amount: Enter the total amount you plan to borrow. This is usually the purchase price of the home minus your down payment.
Annual Interest Rate: Input the yearly interest rate you expect for your mortgage. This is often expressed as a percentage (e.g., 5.0 for 5%).
Loan Term (Years): Specify how many years you intend to take to repay the loan (e.g., 15, 30).
Calculate Payment: Click the "Calculate Payment" button.
The calculator will then display your estimated monthly principal and interest payment. Remember to factor in other costs like taxes, insurance, and potential PMI for a complete picture of your housing expenses.
Example Calculation
Let's say you are considering a mortgage with the following details:
Loan Amount (P): $250,000
Annual Interest Rate: 5.5%
Loan Term: 30 Years
First, we convert these to the required variables:
This calculation yields an estimated monthly payment (P&I) of approximately $1,419.37.
Factors Affecting Your Actual Payment
Your actual mortgage payment can vary based on:
Lender Fees: Origination fees, points, and other closing costs.
Escrow Accounts: Payments for property taxes and homeowner's insurance can fluctuate annually.
Private Mortgage Insurance (PMI): Required if your down payment is less than 20%.
Adjustable-Rate Mortgages (ARMs): Interest rates can change over time, affecting your monthly payment.
Property Taxes and Insurance Changes: These can increase or decrease over the life of the loan.
function calculateMortgage() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var loanTermYears = parseFloat(document.getElementById("loanTermYears").value);
var resultDiv = document.getElementById("result");
var resultValueSpan = document.getElementById("result-value");
// Clear previous results and error messages
resultDiv.style.display = "none";
resultValueSpan.textContent = "$0.00";
// Input validation
if (isNaN(loanAmount) || loanAmount <= 0) {
alert("Please enter a valid Loan Amount greater than 0.");
return;
}
if (isNaN(annualInterestRate) || annualInterestRate <= 0) {
alert("Please enter a valid Annual Interest Rate greater than 0.");
return;
}
if (isNaN(loanTermYears) || loanTermYears <= 0) {
alert("Please enter a valid Loan Term in Years greater than 0.");
return;
}
var monthlyInterestRate = annualInterestRate / 100 / 12;
var numberOfPayments = loanTermYears * 12;
var monthlyPayment = 0;
// Handle the edge case where interest rate is effectively zero
if (monthlyInterestRate === 0) {
monthlyPayment = loanAmount / numberOfPayments;
} else {
var numerator = monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments);
var denominator = Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1;
monthlyPayment = loanAmount * (numerator / denominator);
}
// Format the result to two decimal places
var formattedMonthlyPayment = monthlyPayment.toFixed(2);
resultValueSpan.textContent = "$" + formattedMonthlyPayment;
resultDiv.style.display = "block";
}