Amortization Schedule Calculator
body {
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background-color: #f8f9fa;
color: #333;
line-height: 1.6;
margin: 0;
padding: 20px;
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.loan-calc-container {
max-width: 900px;
margin: 30px auto;
background-color: #ffffff;
padding: 30px;
border-radius: 8px;
box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
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h1, h2 {
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text-align: center;
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#result span {
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.amortization-table {
width: 100%;
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}
Amortization Schedule Calculator
Amortization Schedule
Enter loan details above and click "Generate Schedule" to see the amortization table.
Understanding Amortization Schedules
An amortization schedule is a table that details each periodic payment on an amortizing loan (like a mortgage or auto loan). For each payment, it shows how much of the payment goes towards the principal balance and how much goes towards interest, as well as the remaining balance after the payment is made.
How it Works: The Math Behind Amortization
The core of an amortization schedule is calculating the fixed periodic payment and then breaking down each payment into its interest and principal components. The formulas involved are:
1. Calculating the Monthly Payment (M):
The standard formula for calculating the monthly payment on an amortizing loan is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
- P = Principal loan amount
- i = Monthly interest rate (Annual rate / 12)
- n = Total number of payments (Loan term in years * 12)
2. Calculating Interest and Principal for Each Payment:
For each payment period:
- Interest Paid = Remaining Balance * Monthly Interest Rate (i)
- Principal Paid = Monthly Payment (M) – Interest Paid
- New Remaining Balance = Remaining Balance – Principal Paid
This process repeats for every payment until the loan balance reaches zero.
Key Components of an Amortization Schedule:
- Payment Number: The sequence of the payment (1, 2, 3, …).
- Payment Date: The date each payment is due.
- Starting Balance: The loan balance at the beginning of the payment period.
- Total Payment: The fixed amount paid each period (calculated above).
- Interest Paid: The portion of the payment that covers interest.
- Principal Paid: The portion of the payment that reduces the loan principal.
- Ending Balance: The loan balance after the payment is applied.
Why Use an Amortization Schedule?
Understanding your amortization schedule is crucial for several reasons:
- Financial Planning: It helps you budget accurately by knowing your fixed monthly payments.
- Loan Comparison: You can compare different loan offers by looking at the total interest paid over the life of the loan. Loans with lower interest rates or shorter terms will result in less total interest.
- Early Payoff Strategy: By seeing how much principal is paid down each month, you can strategize about making extra payments to pay off your loan faster and save significantly on interest. Early payments typically go towards the principal, accelerating the payoff.
- Transparency: It provides a clear breakdown of where your money is going, ensuring you understand the cost of borrowing.
This calculator provides a detailed view of your loan's journey, empowering you with financial clarity.
function calculateAmortization() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var loanTermYears = parseInt(document.getElementById("loanTermYears").value);
var resultDiv = document.getElementById("result");
var tableContainer = document.getElementById("amortizationTableContainer");
tableContainer.innerHTML = "; // Clear previous table
if (isNaN(loanAmount) || isNaN(annualInterestRate) || isNaN(loanTermYears) || loanAmount <= 0 || annualInterestRate < 0 || loanTermYears <= 0) {
resultDiv.innerHTML = '
Please enter valid positive numbers for all fields.';
return;
}
var monthlyInterestRate = annualInterestRate / 100 / 12;
var numberOfPayments = loanTermYears * 12;
// Calculate monthly payment
var monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
if (isNaN(monthlyPayment) || !isFinite(monthlyPayment)) {
resultDiv.innerHTML = '
Could not calculate monthly payment. Check input values.';
return;
}
resultDiv.innerHTML = "Estimated Monthly Payment:
$" + monthlyPayment.toFixed(2) + "";
// Build the amortization table
var table = '
| Payment # | Date | Starting Balance | Payment | Interest Paid | Principal Paid | Ending Balance |
|---|
';
var currentBalance = loanAmount;
var totalInterestPaid = 0;
var totalPrincipalPaid = 0;
for (var i = 1; i <= numberOfPayments; i++) {
var interestPayment = currentBalance * monthlyInterestRate;
var principalPayment = monthlyPayment – interestPayment;
// Adjust last payment to ensure balance is exactly zero
if (i === numberOfPayments) {
principalPayment = currentBalance;
monthlyPayment = interestPayment + principalPayment; // Recalculate final payment
}
var endingBalance = currentBalance – principalPayment;
// Handle potential floating point inaccuracies for the last payment
if (endingBalance -0.01) {
endingBalance = 0;
}
totalInterestPaid += interestPayment;
totalPrincipalPaid += principalPayment;
// Format date (simple representation)
var paymentDate = new Date();
paymentDate.setMonth(paymentDate.getMonth() + i -1); // Approximate date
var formattedDate = (paymentDate.getMonth() + 1) + "/" + paymentDate.getDate() + "/" + paymentDate.getFullYear();
table += '';
table += '| ' + i + ' | ';
table += '' + formattedDate + ' | ';
table += '$' + currentBalance.toFixed(2) + ' | ';
table += '$' + monthlyPayment.toFixed(2) + ' | ';
table += '$' + interestPayment.toFixed(2) + ' | ';
table += '$' + principalPayment.toFixed(2) + ' | ';
table += '$' + endingBalance.toFixed(2) + ' | ';
table += '
';
currentBalance = endingBalance;
}
table += '
';
table += 'Total Interest Paid:
$' + totalInterestPaid.toFixed(2) + '';
table += 'Total Principal Paid:
$' + totalPrincipalPaid.toFixed(2) + '';
tableContainer.innerHTML = table;
}