Mortgage Payment Calculator
Understanding Your Mortgage Payment
A mortgage is a loan used to purchase real estate. The monthly mortgage payment typically consists of four main components, often referred to as PITI:
- Principal: The amount you borrowed to buy the property.
- Interest: The cost of borrowing the money, calculated as a percentage of the outstanding loan balance.
- Taxes: Property taxes assessed by your local government. These are usually paid into an escrow account managed by your lender and paid out on your behalf when due.
- Insurance: Homeowners insurance premiums, which protect against damage to your property. Lenders also often require flood insurance if the property is in a flood zone. Similar to taxes, these are usually paid into an escrow account.
The calculator above focuses on the Principal and Interest (P&I) portion of your monthly payment. The formula used is the standard monthly payment formula for an amortizing loan:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
M = Your total monthly mortgage payment (Principal & Interest)P = The loan principal (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: If you take out a $200,000 loan at 5% annual interest for 30 years, your estimated monthly Principal & Interest payment would be approximately $1,073.64.
function calculateMortgage() {
var principal = document.getElementById("principal").value;
var interestRate = document.getElementById("interestRate").value;
var loanTerm = document.getElementById("loanTerm").value;
var resultDiv = document.getElementById("result");
// Input validation
if (principal === "" || interestRate === "" || loanTerm === "") {
resultDiv.innerHTML = "Please fill in all fields.";
return;
}
principal = parseFloat(principal);
interestRate = parseFloat(interestRate);
loanTerm = parseFloat(loanTerm);
if (isNaN(principal) || isNaN(interestRate) || isNaN(loanTerm) || principal <= 0 || interestRate < 0 || loanTerm <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// Calculate monthly interest rate
var monthlyInterestRate = (interestRate / 100) / 12;
// Calculate total number of payments
var numberOfPayments = loanTerm * 12;
// Calculate the monthly payment using the mortgage formula
var monthlyPayment = principal * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
// Display the result, formatted to two decimal places
resultDiv.innerHTML = "Estimated Monthly Payment (Principal & Interest):
$" + monthlyPayment.toFixed(2) + "";
}
.calculator-container {
font-family: Arial, sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ccc;
border-radius: 8px;
background-color: #f9f9f9;
}
.calculator-container h2 {
text-align: center;
margin-bottom: 20px;
color: #333;
}
.calculator-inputs {
display: grid;
grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
gap: 15px;
margin-bottom: 20px;
}
.input-group {
display: flex;
flex-direction: column;
}
.input-group label {
margin-bottom: 5px;
font-weight: bold;
color: #555;
}
.input-group input[type="number"] {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
}
.calculator-inputs button {
grid-column: 1 / -1; /* Span across all columns */
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
cursor: pointer;
transition: background-color 0.3s ease;
}
.calculator-inputs button:hover {
background-color: #0056b3;
}
#result {
margin-top: 20px;
padding: 15px;
background-color: #e9ecef;
border: 1px solid #dee2e6;
border-radius: 4px;
text-align: center;
font-size: 1.1em;
}
#result strong {
color: #28a745;
}
.calculator-explanation {
margin-top: 30px;
border-top: 1px solid #eee;
padding-top: 20px;
}
.calculator-explanation h3 {
color: #333;
margin-bottom: 15px;
}
.calculator-explanation p, .calculator-explanation ul {
color: #555;
line-height: 1.6;
}
.calculator-explanation ul {
margin-left: 20px;
}
.calculator-explanation code {
background-color: #e0e0e0;
padding: 2px 4px;
border-radius: 3px;
font-family: monospace;
}