Mortgage Payment Calculator
Your Estimated Monthly Payment:
Understanding Your Mortgage Payment
A mortgage is a type of loan used to purchase a home or other real estate. The borrower agrees to pay the lender back over a period of time, typically 15 to 30 years, with interest. The monthly mortgage payment is usually the largest expense for homeowners and is calculated based on several key factors:
Loan Amount:
This is the total amount of money you are borrowing from the lender to buy your property. It's the principal amount of the loan, excluding any down payment you might make.
Annual Interest Rate:
This is the yearly percentage charged by the lender for borrowing the money. A lower interest rate means you'll pay less in interest over the life of the loan. Interest rates can fluctuate based on market conditions and your creditworthiness.
Loan Term (in Years):
This is the total duration over which you agree to repay the loan. Common terms are 15 or 30 years. A shorter loan term will result in higher monthly payments but less interest paid overall. A longer loan term means lower monthly payments but more interest paid over time.
The Mortgage Payment Formula:
The standard formula used to calculate the fixed monthly payment (M) for a mortgage 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)
Example Calculation:
Let's say you're looking to buy a home and secure a mortgage with the following details:
- Loan Amount (P): $300,000
- Annual Interest Rate: 5%
- Loan Term: 30 years
First, we need to calculate the monthly interest rate (i) and the total number of payments (n):
- Monthly Interest Rate (i) = 5% / 12 / 100 = 0.05 / 12 ≈ 0.00416667
- Total Number of Payments (n) = 30 years * 12 months/year = 360
Now, plugging these values into the formula:
M = 300,000 [ 0.00416667(1 + 0.00416667)^360 ] / [ (1 + 0.00416667)^360 – 1]
M ≈ 300,000 [ 0.00416667 * (1.00416667)^360 ] / [ (1.00416667)^360 – 1 ]
M ≈ 300,000 [ 0.00416667 * 4.467744 ] / [ 4.467744 – 1 ]
M ≈ 300,000 [ 0.0186156 ] / [ 3.467744 ]
M ≈ 300,000 * 0.0053682
M ≈ $1,610.46
So, the estimated monthly mortgage payment for this example would be approximately $1,610.46. Remember that this calculation typically covers only the principal and interest (P&I). Your actual total monthly housing payment may also include property taxes, homeowner's insurance (and potentially private mortgage insurance – PMI), which are often paid into an escrow account.
var calculateMortgage = function() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var loanTermYears = parseFloat(document.getElementById("loanTermYears").value);
var errorMessageDiv = document.getElementById("errorMessage");
var resultDiv = document.getElementById("result");
errorMessageDiv.textContent = ""; // Clear previous errors
resultDiv.innerHTML = '$0.00'; // Clear previous results
if (isNaN(loanAmount) || isNaN(annualInterestRate) || isNaN(loanTermYears) || loanAmount <= 0 || annualInterestRate < 0 || loanTermYears <= 0) {
errorMessageDiv.textContent = "Please enter valid positive numbers for all fields.";
return;
}
var monthlyInterestRate = (annualInterestRate / 100) / 12;
var numberOfPayments = loanTermYears * 12;
// Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
var numerator = monthlyInterestRate * Math.pow((1 + monthlyInterestRate), numberOfPayments);
var denominator = Math.pow((1 + monthlyInterestRate), numberOfPayments) – 1;
if (denominator === 0) { // Avoid division by zero, though unlikely with valid inputs
errorMessageDiv.textContent = "Calculation error. Please check your inputs.";
return;
}
var monthlyPayment = loanAmount * (numerator / denominator);
resultDiv.innerHTML = '$' + monthlyPayment.toFixed(2) + '';
};
.calculator-container {
font-family: sans-serif;
border: 1px solid #ccc;
padding: 20px;
border-radius: 8px;
max-width: 600px;
margin: 20px auto;
background-color: #f9f9f9;
}
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display: grid;
grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
gap: 15px;
margin-bottom: 20px;
}
.input-group {
display: flex;
flex-direction: column;
}
.input-group label {
margin-bottom: 5px;
font-weight: bold;
color: #333;
}
.input-group input[type="number"] {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 1rem;
}
button {
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
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transition: background-color 0.3s ease;
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}
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background-color: #0056b3;
}
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text-align: center;
margin-top: 20px;
padding: 15px;
background-color: #e9ecef;
border-radius: 4px;
}
.calculator-results h3 {
margin-top: 0;
color: #555;
}
#result p {
font-size: 1.8rem;
font-weight: bold;
color: #28a745;
margin: 10px 0;
}
.calculator-explanation {
font-family: sans-serif;
margin: 30px auto;
padding: 20px;
max-width: 800px;
line-height: 1.6;
color: #333;
}
.calculator-explanation h2,
.calculator-explanation h3 {
color: #007bff;
margin-top: 20px;
}
.calculator-explanation ul {
margin-left: 20px;
margin-bottom: 15px;
}
.calculator-explanation li {
margin-bottom: 8px;
}
.calculator-explanation strong {
color: #0056b3;
}