Advanced Mortgage Amortization Calculator
body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
max-width: 1200px;
margin: 0 auto;
padding: 20px;
background-color: #f4f7f6;
}
.calculator-wrapper {
background: #ffffff;
border-radius: 12px;
box-shadow: 0 4px 20px rgba(0,0,0,0.1);
padding: 40px;
margin-bottom: 50px;
display: flex;
flex-wrap: wrap;
gap: 40px;
}
.calc-inputs {
flex: 1;
min-width: 300px;
}
.calc-results {
flex: 1;
min-width: 300px;
background-color: #f8f9fa;
border-radius: 8px;
padding: 30px;
border: 1px solid #e9ecef;
}
.input-group {
margin-bottom: 20px;
}
.input-group label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #2c3e50;
}
.input-group input, .input-group select {
width: 100%;
padding: 12px;
border: 2px solid #ddd;
border-radius: 6px;
font-size: 16px;
transition: border-color 0.3s;
box-sizing: border-box;
}
.input-group input:focus {
border-color: #3498db;
outline: none;
}
.calc-btn {
width: 100%;
padding: 15px;
background-color: #2c3e50;
color: white;
border: none;
border-radius: 6px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s;
}
.calc-btn:hover {
background-color: #34495e;
}
.result-row {
display: flex;
justify-content: space-between;
align-items: center;
margin-bottom: 15px;
padding-bottom: 15px;
border-bottom: 1px solid #dee2e6;
}
.result-row:last-child {
border-bottom: none;
}
.result-label {
color: #6c757d;
font-size: 14px;
}
.result-value {
font-size: 20px;
font-weight: 700;
color: #2c3e50;
}
.highlight-result {
color: #27ae60;
font-size: 28px;
}
.content-section {
background: #fff;
padding: 40px;
border-radius: 12px;
box-shadow: 0 2px 10px rgba(0,0,0,0.05);
}
h1 { color: #2c3e50; margin-bottom: 10px; }
h2 { color: #34495e; margin-top: 30px; margin-bottom: 15px; }
p { margin-bottom: 15px; }
ul { margin-bottom: 20px; padding-left: 20px; }
li { margin-bottom: 8px; }
.disclaimer {
font-size: 12px;
color: #999;
margin-top: 20px;
text-align: center;
}
@media (max-width: 768px) {
.calculator-wrapper {
flex-direction: column;
padding: 20px;
}
}
Repayment Summary
Estimated Monthly Payment
$0.00
Loan Amount (Principal)
$0.00
Total Interest Paid
$0.00
Total Cost of Loan
$0.00
Payoff Date
–
Mortgage Amortization Calculator
Understanding how your mortgage works is the first step toward financial freedom. This specific Mortgage Amortization Calculator is designed to help prospective homeowners and real estate investors analyze the true cost of borrowing. By inputting your home price, down payment, interest rate, and loan term, you can instantly visualize your monthly financial commitment and the long-term impact of interest.
How Mortgage Amortization Works
Amortization is the process of spreading out a loan into a series of fixed payments over time. While your total monthly payment remains the same, the portion that goes toward principal (the actual loan balance) and interest (the cost of borrowing) changes every month.
- Early Years: In the beginning of a 30-year mortgage, the majority of your payment goes toward interest. This is why the loan balance decreases very slowly at first.
- Later Years: As the principal balance drops, less interest accrues, meaning more of your fixed payment is applied to the principal, accelerating equity build-up.
Factors That Impact Your Monthly Payment
When using this calculator, consider how small adjustments can lead to significant savings:
- Down Payment: A larger down payment reduces the principal loan amount. This not only lowers your monthly payment but can also eliminate the need for Private Mortgage Insurance (PMI) if you put down at least 20%.
- Interest Rate: Even a 0.5% difference in your interest rate can save—or cost—you tens of thousands of dollars over the life of the loan. Improving your credit score is the best way to secure a lower rate.
- Loan Term: A 15-year term will have higher monthly payments compared to a 30-year term, but the total interest paid will be drastically lower. Use the "Loan Term" dropdown in the calculator to compare these scenarios.
Principal vs. Interest: The Real Cost
Many homebuyers focus solely on the monthly payment, ignoring the "Total Interest Paid" metric. This is a mistake. For example, on a $300,000 loan at 7% interest over 30 years, you might pay over $400,000 in interest alone—more than the original value of the home.
To reduce this cost, consider making extra payments toward the principal. Even one extra payment a year can shave years off your loan term and save massive amounts in interest.
How to Use This Calculator
To get the most accurate results:
- Home Price: Enter the purchase price of the property.
- Down Payment: Input the cash amount you plan to pay upfront.
- Interest Rate: Enter the current annual percentage rate (APR) you expect to qualify for.
- Loan Term: Select the duration of the mortgage (commonly 15 or 30 years).
The results will instantly update to show your estimated monthly principal and interest payment, along with the total cost of the loan over time.
function calculateMortgage() {
// 1. Get Input Values
var priceInput = document.getElementById('homePrice');
var downInput = document.getElementById('downPayment');
var rateInput = document.getElementById('interestRate');
var termInput = document.getElementById('loanTerm');
var price = parseFloat(priceInput.value);
var down = parseFloat(downInput.value);
var rate = parseFloat(rateInput.value);
var years = parseFloat(termInput.value);
// 2. Validate Inputs
if (isNaN(price) || isNaN(down) || isNaN(rate) || isNaN(years)) {
alert("Please ensure all fields contain valid numbers.");
return;
}
if (down > price) {
alert("Down payment cannot be greater than the home price.");
return;
}
// 3. Perform Calculations
var principal = price – down;
var monthlyRate = rate / 100 / 12;
var totalPayments = years * 12;
var monthlyPayment = 0;
// Handle zero interest case
if (rate === 0) {
monthlyPayment = principal / totalPayments;
} else {
// Standard Amortization Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
var x = Math.pow(1 + monthlyRate, totalPayments);
monthlyPayment = (principal * x * monthlyRate) / (x – 1);
}
var totalRepayment = monthlyPayment * totalPayments;
var totalInterest = totalRepayment – principal;
// Calculate Payoff Date
var today = new Date();
var payoffDate = new Date(today.setMonth(today.getMonth() + totalPayments));
var monthNames = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
var payoffString = monthNames[payoffDate.getMonth()] + " " + payoffDate.getFullYear();
// 4. Update UI
// Helper function for currency formatting
function formatCurrency(num) {
return "$" + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
document.getElementById('monthlyPaymentDisplay').innerHTML = formatCurrency(monthlyPayment);
document.getElementById('loanAmountDisplay').innerHTML = formatCurrency(principal);
document.getElementById('totalInterestDisplay').innerHTML = formatCurrency(totalInterest);
document.getElementById('totalCostDisplay').innerHTML = formatCurrency(totalRepayment);
document.getElementById('payoffDateDisplay').innerHTML = payoffString;
}
// Run calculation on load to show initial state
window.onload = function() {
calculateMortgage();
};