#mortgage-calculator-wrapper {
font-family: sans-serif;
border: 1px solid #ccc;
padding: 20px;
border-radius: 8px;
max-width: 500px;
margin: 20px auto;
background-color: #f9f9f9;
}
#mortgage-calculator-wrapper h2 {
text-align: center;
color: #333;
margin-bottom: 20px;
}
.mortgage-input-group {
margin-bottom: 15px;
display: flex;
align-items: center;
justify-content: space-between;
}
.mortgage-input-group label {
flex: 1;
margin-right: 10px;
color: #555;
font-weight: bold;
}
.mortgage-input-group input[type="number"],
.mortgage-input-group input[type="text"] {
flex: 1.5;
padding: 8px;
border: 1px solid #ddd;
border-radius: 4px;
box-sizing: border-box; /* Ensure padding doesn't affect width */
}
.mortgage-input-group input[type="number"] {
text-align: right;
}
#calculate-mortgage-btn {
display: block;
width: 100%;
padding: 10px 15px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
cursor: pointer;
font-size: 16px;
margin-top: 20px;
transition: background-color 0.3s ease;
}
#calculate-mortgage-btn:hover {
background-color: #0056b3;
}
#mortgage-result {
margin-top: 25px;
padding: 15px;
background-color: #e9ecef;
border-radius: 4px;
border: 1px solid #ced4da;
text-align: center;
font-size: 18px;
font-weight: bold;
color: #333;
}
#mortgage-result p {
margin: 5px 0;
}
#mortgage-result .label {
font-weight: normal;
color: #666;
}
function calculateMortgage() {
var loanAmountInput = document.getElementById("loanAmount");
var annualInterestRateInput = document.getElementById("annualInterestRate");
var loanTermYearsInput = document.getElementById("loanTermYears");
var loanAmount = parseFloat(loanAmountInput.value);
var annualInterestRate = parseFloat(annualInterestRateInput.value);
var loanTermYears = parseFloat(loanTermYearsInput.value);
var monthlyPaymentResult = document.getElementById("monthlyPaymentResult");
var totalPrincipalResult = document.getElementById("totalPrincipalResult");
var totalInterestResult = document.getElementById("totalInterestResult");
var totalRepaymentResult = document.getElementById("totalRepaymentResult");
// Clear previous results
monthlyPaymentResult.textContent = "–";
totalPrincipalResult.textContent = "–";
totalInterestResult.textContent = "–";
totalRepaymentResult.textContent = "–";
// Input validation
if (isNaN(loanAmount) || loanAmount <= 0) {
alert("Please enter a valid loan amount greater than zero.");
return;
}
if (isNaN(annualInterestRate) || annualInterestRate < 0) {
alert("Please enter a valid annual interest rate.");
return;
}
if (isNaN(loanTermYears) || loanTermYears 0) {
monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
} else {
// Handle zero interest rate case
monthlyPayment = loanAmount / numberOfPayments;
}
var totalRepayment = monthlyPayment * numberOfPayments;
var totalInterestPaid = totalRepayment – loanAmount;
// Display results
monthlyPaymentResult.textContent = "$" + monthlyPayment.toFixed(2);
totalPrincipalResult.textContent = loanAmount.toFixed(2);
totalInterestResult.textContent = totalInterestPaid.toFixed(2);
totalRepaymentResult.textContent = totalRepayment.toFixed(2);
}
Understanding Your Mortgage Payment
A mortgage is a significant financial commitment, often the largest loan most people will ever take out. It's crucial to understand how your monthly mortgage payment is calculated. This calculator helps demystify the process by breaking down the key components: the loan principal, the interest rate, and the loan term.
Loan Amount (Principal)
This is the total amount of money you are borrowing from the lender to purchase your home. It's the initial balance of your mortgage.
Annual Interest Rate
The interest rate is the cost of borrowing money, expressed as a percentage of the loan amount. A lower interest rate means you'll pay less in interest over the life of the loan. This rate can be fixed (stays the same for the entire loan term) or variable (can change over time).
Loan Term (Years)
The loan term is the length of time you have to repay the mortgage. Common terms are 15, 20, or 30 years. A shorter loan term generally results in higher monthly payments but lower total interest paid. A longer loan term means lower monthly payments but more interest paid overall.
The Monthly Payment Formula (P&I)
The most common mortgage payment calculation uses an amortization formula to determine your principal and interest (P&I) payment. The formula ensures that each payment includes a portion that goes towards reducing the principal balance and a portion that covers the interest accrued. Over time, the proportion of your payment applied to interest decreases, while the proportion applied to the principal increases.
The standard formula for calculating the monthly mortgage payment (M) is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
M = Your total monthly mortgage paymentP = Your loan principal (the amount you borrow)i = Your monthly interest rate (annual rate divided by 12)n = Your total number of payments (loan term in years multiplied by 12)
This calculator uses this formula to provide your estimated monthly P&I payment. Keep in mind that your actual total monthly housing expense may also include property taxes, homeowner's insurance, and potentially private mortgage insurance (PMI) or homeowners association (HOA) fees, which are not factored into this specific calculation.
Example Calculation:
Let's say you are buying a home and need a mortgage with the following terms:
- Loan Amount (P): $250,000
- Annual Interest Rate: 4.0%
- Loan Term: 30 years
Using the calculator:
- Monthly Interest Rate (i): 4.0% / 12 / 100 = 0.003333…
- Number of Payments (n): 30 years * 12 months/year = 360
The calculator would determine:
- Estimated Monthly Payment: Approximately $1,193.54
- Total Principal Paid: $250,000.00
- Total Interest Paid: Approximately $179,675.17
- Total Repayment: Approximately $429,675.17
Understanding these figures helps you budget effectively and make informed decisions about your homeownership journey.