:root {
–primary-blue: #004a99;
–success-green: #28a745;
–light-background: #f8f9fa;
–border-color: #dee2e6;
–text-color: #333;
–label-color: #555;
}
body {
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
background-color: var(–light-background);
color: var(–text-color);
line-height: 1.6;
margin: 0;
padding: 20px;
}
.loan-calc-container {
max-width: 800px;
margin: 40px auto;
background-color: #ffffff;
padding: 30px;
border-radius: 8px;
box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
border: 1px solid var(–border-color);
}
h1, h2 {
color: var(–primary-blue);
text-align: center;
margin-bottom: 20px;
}
.input-group {
margin-bottom: 20px;
display: flex;
flex-direction: column;
align-items: flex-start;
}
.input-group label {
display: block;
margin-bottom: 8px;
font-weight: bold;
color: var(–label-color);
font-size: 0.95em;
}
.input-group input[type="number"],
.input-group input[type="text"],
.input-group select {
width: calc(100% – 22px); /* Adjust for padding and border */
padding: 10px 10px;
border: 1px solid var(–border-color);
border-radius: 5px;
font-size: 1em;
box-sizing: border-box; /* Include padding and border in the element's total width and height */
}
.input-group input:focus,
.input-group select:focus {
outline: none;
border-color: var(–primary-blue);
box-shadow: 0 0 0 3px rgba(0, 74, 153, 0.2);
}
.button-group {
text-align: center;
margin-top: 25px;
margin-bottom: 30px;
}
.calculate-button {
background-color: var(–primary-blue);
color: white;
padding: 12px 25px;
border: none;
border-radius: 5px;
font-size: 1.1em;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s ease, transform 0.2s ease;
}
.calculate-button:hover {
background-color: #003f87; /* Darker blue */
transform: translateY(-2px);
}
.result-container {
margin-top: 30px;
padding: 25px;
background-color: var(–success-green); /* Success green for emphasis */
color: white;
border-radius: 5px;
text-align: center;
box-shadow: inset 0 0 10px rgba(0,0,0,0.1);
}
.result-container h3 {
margin-top: 0;
color: white;
font-size: 1.3em;
margin-bottom: 15px;
}
.result-container #monthlyPayment,
.result-container #totalInterest {
font-size: 2em;
font-weight: bold;
display: block;
margin-bottom: 10px;
}
.result-container span {
font-size: 0.9em;
opacity: 0.9;
}
.article-section {
margin-top: 40px;
padding-top: 20px;
border-top: 1px solid var(–border-color);
}
.article-section h2 {
color: var(–primary-blue);
margin-bottom: 15px;
font-size: 1.8em;
}
.article-section p {
margin-bottom: 15px;
color: var(–text-color);
}
.article-section ul {
list-style-type: disc;
margin-left: 20px;
margin-bottom: 15px;
}
.article-section li {
margin-bottom: 8px;
}
/* Responsive adjustments */
@media (max-width: 600px) {
.loan-calc-container {
padding: 20px;
margin: 20px auto;
}
.calculate-button {
padding: 10px 20px;
font-size: 1em;
}
.result-container {
padding: 20px;
}
.result-container #monthlyPayment,
.result-container #totalInterest {
font-size: 1.7em;
}
.article-section h2 {
font-size: 1.5em;
}
}
Understanding Your Mortgage Payment
A mortgage is a significant financial commitment, and understanding how your monthly payment is calculated is crucial. This calculator helps demystify the process by breaking down the principal and interest components of your loan. The primary formula used is the standard annuity formula for loan payments.
The Mortgage Payment Formula
The monthly mortgage payment (M) is calculated using the following formula:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
- P = Principal loan amount (the total amount you borrow)
- i = Monthly interest rate (annual rate divided by 12)
- n = Total number of payments (loan term in years multiplied by 12)
How it Works
The formula ensures that over the life of the loan, you pay off both the principal amount borrowed and the accumulated interest. In the early years of a mortgage, a larger portion of your payment goes towards interest. As the loan matures, more of your payment is applied to the principal. This is known as amortization.
Key Terms Explained:
- Loan Amount (Principal): This is the total sum of money you borrow to purchase your home.
- Annual Interest Rate: This is the yearly percentage charged by the lender for borrowing the money. For calculation purposes, it's converted into a monthly rate by dividing by 12.
- Loan Term (Years): This is the total duration over which you agree to repay the loan. Common terms are 15, 20, or 30 years. This is converted into the total number of monthly payments.
- Monthly Payment: This is the fixed amount you pay each month to your lender, covering both principal and interest.
- Total Interest Paid: This is the sum of all interest payments made over the entire life of the loan. It's calculated by subtracting the original loan amount from the total amount paid (monthly payment multiplied by the total number of payments).
Example Calculation
Let's say you're considering a mortgage with the following details:
- Loan Amount (P): $300,000
- Annual Interest Rate: 3.5%
- 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) = 3.5% / 12 = 0.035 / 12 ≈ 0.00291667
- Total Number of Payments (n) = 30 years * 12 months/year = 360
Now, plug these values into the formula:
M = 300000 [ 0.00291667(1 + 0.00291667)^360 ] / [ (1 + 0.00291667)^360 – 1]
M ≈ 300000 [ 0.00291667 * (1.00291667)^360 ] / [ (1.00291667)^360 – 1]
M ≈ 300000 [ 0.00291667 * 2.8177 ] / [ 2.8177 – 1]
M ≈ 300000 [ 0.0082165 ] / [ 1.8177 ]
M ≈ 300000 * 0.004520
M ≈ $1,350.58
The estimated monthly payment would be approximately $1,350.58.
To calculate the total interest paid:
Total Paid = Monthly Payment * Total Number of Payments
Total Paid = $1,350.58 * 360 ≈ $486,208.80
Total Interest Paid = Total Paid – Loan Amount
Total Interest Paid = $486,208.80 – $300,000 = $186,208.80
This calculator simplifies this process, providing instant estimates for your potential mortgage payments. Remember that this calculation typically excludes property taxes, homeowners insurance, and Private Mortgage Insurance (PMI), which may also be included in your actual monthly housing expense (often referred to as PITI: Principal, Interest, Taxes, Insurance).
function calculateMortgage() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var loanTermYears = parseInt(document.getElementById("loanTermYears").value);
var resultContainer = document.getElementById("resultContainer");
var monthlyPaymentSpan = document.getElementById("monthlyPayment");
var totalInterestSpan = document.getElementById("totalInterest");
// Clear previous results
monthlyPaymentSpan.textContent = "–";
totalInterestSpan.textContent = "–";
resultContainer.style.display = 'none';
// Input validation
if (isNaN(loanAmount) || loanAmount <= 0 ||
isNaN(annualInterestRate) || annualInterestRate < 0 ||
isNaN(loanTermYears) || loanTermYears <= 0) {
alert("Please enter valid numbers for all fields. Loan amount and term must be positive, and interest rate cannot be negative.");
return;
}
var monthlyInterestRate = annualInterestRate / 100 / 12;
var numberOfPayments = loanTermYears * 12;
var monthlyPayment = 0;
var totalInterest = 0;
// Calculate monthly payment using the annuity formula
if (monthlyInterestRate === 0) {
// Handle zero interest rate case
monthlyPayment = loanAmount / numberOfPayments;
} else {
monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
}
// Calculate total interest
var totalAmountPaid = monthlyPayment * numberOfPayments;
totalInterest = totalAmountPaid – loanAmount;
// Format and display results
monthlyPaymentSpan.textContent = "$" + monthlyPayment.toFixed(2);
totalInterestSpan.textContent = "$" + totalInterest.toFixed(2);
resultContainer.style.display = 'block';
}