Mortgage Payment Calculator
A mortgage is a type of loan used to purchase real estate, such as a home. The borrower agrees to pay the lender back over a period of time, typically 15 to 30 years, with interest. The monthly mortgage payment usually includes principal, interest, taxes, and insurance (often referred to as PITI).
Understanding Your Mortgage Payment
The monthly mortgage payment is calculated using a standard amortization formula. This formula takes into account the principal loan amount, the annual interest rate, and the loan term in years. The interest rate is usually expressed as an annual percentage, but for the calculation, it needs to be converted to a monthly rate (annual rate divided by 12).
The loan term is typically in years, but the calculation requires the total number of monthly payments (loan term in years multiplied by 12).
Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
- M = Your total monthly mortgage payment
- P = Principal loan amount
- i = Monthly interest rate (Annual rate / 12)
- n = Total number of payments (Loan term in years * 12)
It's important to note that this calculator provides an estimate for the principal and interest portion of your mortgage payment. It does not include property taxes, homeowner's insurance, or private mortgage insurance (PMI), which are often included in your total monthly housing expense (PITI).
function calculateMortgage() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var resultDiv = document.getElementById("result");
if (isNaN(loanAmount) || isNaN(interestRate) || isNaN(loanTerm) || loanAmount <= 0 || interestRate < 0 || loanTerm <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
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)) {
resultDiv.innerHTML = "Could not calculate the mortgage payment. Please check your inputs.";
return;
}
resultDiv.innerHTML = "
Estimated Monthly Principal & Interest Payment:
$" + monthlyPayment.toFixed(2) + "";
}
.calculator-container {
font-family: sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ddd;
border-radius: 8px;
background-color: #f9f9f9;
}
.calculator-container h2 {
text-align: center;
color: #333;
margin-bottom: 20px;
}
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grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
gap: 15px;
margin-bottom: 20px;
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.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;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
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cursor: pointer;
transition: background-color 0.3s ease;
}
.calculator-inputs button:hover {
background-color: #0056b3;
}
.calculator-result {
margin-top: 20px;
padding: 15px;
background-color: #e9ecef;
border: 1px solid #ced4da;
border-radius: 4px;
text-align: center;
}
.calculator-result h3 {
margin-top: 0;
color: #333;
}
.calculator-result p {
font-size: 24px;
color: #28a745;
font-weight: bold;
}
.calculator-explanation {
margin-top: 30px;
padding-top: 20px;
border-top: 1px solid #eee;
font-size: 14px;
line-height: 1.6;
color: #666;
}
.calculator-explanation h3 {
color: #333;
margin-bottom: 10px;
}
.calculator-explanation ul {
padding-left: 20px;
}
.calculator-explanation li {
margin-bottom: 5px;
}