Understanding your mortgage payment is crucial when buying a home. This calculator helps you estimate your monthly mortgage payment, excluding taxes, insurance, and HOA fees. A mortgage payment is primarily composed of principal and interest (P&I). The principal is the amount borrowed, while the interest is the cost of borrowing that money. The amortization of a loan means that over time, a larger portion of your payment goes towards the principal.
The formula used to calculate the monthly mortgage payment (M) is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
P = Principal loan amount
i = Monthly interest rate (Annual rate divided by 12)
n = Total number of payments (Loan term in years multiplied by 12)
Mortgage Payment Calculator
function calculateMortgage() {
var principal = parseFloat(document.getElementById("principal").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var loanTermYears = parseFloat(document.getElementById("loanTermYears").value);
var mortgageResultDiv = document.getElementById("mortgageResult");
// Clear previous results and error messages
mortgageResultDiv.innerHTML = "";
// Validate inputs
if (isNaN(principal) || principal <= 0) {
mortgageResultDiv.innerHTML = "Please enter a valid loan amount.";
return;
}
if (isNaN(annualInterestRate) || annualInterestRate <= 0) {
mortgageResultDiv.innerHTML = "Please enter a valid annual interest rate.";
return;
}
if (isNaN(loanTermYears) || loanTermYears <= 0) {
mortgageResultDiv.innerHTML = "Please enter a valid loan term in years.";
return;
}
// Calculate monthly interest rate
var monthlyInterestRate = (annualInterestRate / 100) / 12;
// Calculate the total number of payments
var numberOfPayments = loanTermYears * 12;
// Calculate the monthly mortgage payment using the formula
// M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
var numerator = principal * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments));
var denominator = Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1;
var monthlyPayment = numerator / denominator;
// Display the result
if (isNaN(monthlyPayment) || !isFinite(monthlyPayment)) {
mortgageResultDiv.innerHTML = "Could not calculate. Please check your inputs.";
} else {
mortgageResultDiv.innerHTML = "