Mortgage Payment Calculator
Understanding Your Mortgage Payment
A mortgage is a type of loan used to purchase real estate. The loan is paid back over a period of time, typically 15 to 30 years, with regular payments that include both principal and interest. The monthly payment is determined by three main factors: the loan amount (principal), the annual interest rate, and the loan term (in years).
How the Calculation Works:
The standard formula for calculating a fixed-rate mortgage payment is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
- M = Your total monthly mortgage payment
- P = Your 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:
Let's say you want to buy a house and your loan amount (P) is $300,000. The annual interest rate is 5.5%, and you choose a 30-year loan term.
- Principal (P) = $300,000
- Annual Interest Rate = 5.5%
- Monthly Interest Rate (i) = 5.5% / 12 / 100 = 0.00458333
- Loan Term = 30 years
- Number of Payments (n) = 30 * 12 = 360
Using the formula, your estimated monthly mortgage payment (principal and interest) would be approximately $1,702.98.
This calculator provides an estimate for the principal and interest portion of your mortgage payment. It does not include other costs associated with homeownership, such as property taxes, homeowner's insurance, or private mortgage insurance (PMI), which may be included in your actual total monthly housing expense.
function calculateMortgage() {
var principal = parseFloat(document.getElementById("principal").value);
var annualInterestRate = parseFloat(document.getElementById("interestRate").value);
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
// Input validation
if (isNaN(principal) || principal <= 0) {
resultDiv.innerHTML = "Please enter a valid loan amount greater than zero.";
return;
}
if (isNaN(annualInterestRate) || annualInterestRate < 0) {
resultDiv.innerHTML = "Please enter a valid annual interest rate (0 or greater).";
return;
}
if (isNaN(loanTerm) || loanTerm <= 0) {
resultDiv.innerHTML = "Please enter a valid loan term greater than zero.";
return;
}
var monthlyInterestRate = annualInterestRate / 100 / 12;
var numberOfPayments = loanTerm * 12;
var monthlyPayment = 0;
// Handle the case where interest rate is 0
if (monthlyInterestRate === 0) {
monthlyPayment = principal / numberOfPayments;
} else {
monthlyPayment = principal * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
}
if (isNaN(monthlyPayment) || !isFinite(monthlyPayment)) {
resultDiv.innerHTML = "Calculation error. Please check your inputs.";
return;
}
resultDiv.innerHTML =
"
Estimated Monthly Mortgage Payment (Principal & Interest): $" + monthlyPayment.toFixed(2) + "" +
"
This is an estimate for principal and interest only. It does not include taxes, insurance, or other fees.";
}
.calculator-container {
font-family: sans-serif;
border: 1px solid #ccc;
padding: 20px;
border-radius: 8px;
max-width: 700px;
margin: 20px auto;
background-color: #f9f9f9;
}
.calculator-container h2 {
text-align: center;
margin-bottom: 20px;
color: #333;
}
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display: grid;
grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
gap: 15px;
margin-bottom: 20px;
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}
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padding: 10px;
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font-size: 16px;
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font-size: 18px;
cursor: pointer;
transition: background-color 0.3s ease;
}
.calculator-inputs button:hover {
background-color: #0056b3;
}
.calculator-result {
margin-top: 20px;
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font-size: 18px;
}
.calculator-result strong {
color: #007bff;
}
.calculator-explanation {
margin-top: 30px;
padding-top: 20px;
border-top: 1px solid #eee;
}
.calculator-explanation h3,
.calculator-explanation h4 {
color: #333;
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}
.calculator-explanation p {
line-height: 1.6;
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}
.calculator-explanation ul {
margin-left: 20px;
color: #555;
line-height: 1.6;
}
.calculator-explanation li {
margin-bottom: 8px;
}