Estimate your potential monthly mortgage payment based on loan details.
Your Estimated Monthly Payment: $0.00
Understanding Your Mortgage Payment
A mortgage is a significant financial commitment, and understanding how your monthly payment is calculated is crucial. This calculator provides an estimate of your principal and interest payment. Remember that your actual monthly payment may also include property taxes, homeowner's insurance, and potentially Private Mortgage Insurance (PMI), which are often held in an escrow account by your lender.
The Math Behind the Calculation
The standard formula used to calculate a fixed-rate mortgage payment (P&I) 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 amount you borrow)
i = Your monthly interest rate (annual rate divided by 12)
n = The total number of payments over the loan's lifetime (loan term in years multiplied by 12)
Example Calculation:
Let's say you are taking out a mortgage with the following details:
Loan Amount (P): $300,000
Annual Interest Rate: 6.5%
Loan Term: 30 Years
First, we convert the annual interest rate to a monthly interest rate:
This calculator aims to replicate this calculation.
Factors Affecting Your Actual Mortgage Payment
While this calculator provides a clear estimate for principal and interest, remember that lenders will often include additional costs in your total monthly housing expense:
Property Taxes: Varies by location and property value.
Homeowner's Insurance: Required by lenders to protect against damage.
Private Mortgage Insurance (PMI): Typically required if your down payment is less than 20% of the home's purchase price.
Homeowners Association (HOA) Fees: If applicable to your property.
Always consult with your mortgage lender for a precise Loan Estimate that details all costs associated with your mortgage.
function calculateMortgage() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var resultElement = document.getElementById("result").querySelector("span");
if (isNaN(loanAmount) || isNaN(interestRate) || isNaN(loanTerm) ||
loanAmount <= 0 || interestRate <= 0 || loanTerm <= 0) {
resultElement.textContent = "Invalid input. Please enter positive numbers.";
return;
}
var monthlyInterestRate = interestRate / 100 / 12;
var numberOfPayments = loanTerm * 12;
var monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
if (isNaN(monthlyPayment) || !isFinite(monthlyPayment)) {
resultElement.textContent = "Calculation error. Please check inputs.";
return;
}
resultElement.textContent = "$" + monthlyPayment.toFixed(2);
}
// Optional: Add event listeners to update input values if sliders are implemented later or for initial load.
// For this example, button click is sufficient.