Amortization Schedule Calculator
:root {
–primary-blue: #004a99;
–success-green: #28a745;
–light-background: #f8f9fa;
–white: #ffffff;
–gray-text: #333333;
–border-color: #dee2e6;
}
body {
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
line-height: 1.6;
color: var(–gray-text);
background-color: var(–white);
margin: 0;
padding: 20px;
}
.loan-calc-container {
max-width: 900px;
margin: 20px auto;
background-color: var(–white);
border-radius: 8px;
box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
overflow: hidden;
}
.calculator-header {
background-color: var(–primary-blue);
color: var(–white);
padding: 20px;
text-align: center;
border-bottom: 1px solid var(–border-color);
}
.calculator-header h1 {
margin: 0;
font-size: 24px;
font-weight: 600;
}
.calculator-body {
padding: 30px;
display: flex;
flex-wrap: wrap;
gap: 30px;
}
.input-section {
flex: 1;
min-width: 280px;
}
.input-group {
margin-bottom: 20px;
position: relative;
}
.input-group label {
display: block;
margin-bottom: 8px;
font-weight: 500;
color: var(–primary-blue);
}
.input-group input[type="number"],
.input-group input[type="text"] {
width: 100%;
padding: 12px;
border: 1px solid var(–border-color);
border-radius: 4px;
box-sizing: border-box;
font-size: 16px;
}
.input-group input[type="number"]:focus,
.input-group input[type="text"]:focus {
border-color: var(–primary-blue);
outline: none;
box-shadow: 0 0 0 2px rgba(0, 74, 153, 0.2);
}
.input-group .currency-symbol {
position: absolute;
left: 10px;
top: 38px;
color: var(–gray-text);
pointer-events: none;
font-size: 16px;
}
.input-group .percent-symbol {
position: absolute;
right: 10px;
top: 38px;
color: var(–gray-text);
pointer-events: none;
font-size: 16px;
}
.input-group input[type="number"].with-symbol {
padding-left: 35px; /* For currency symbol */
}
.input-group input[type="number"].with-percent-symbol {
padding-right: 35px; /* For percent symbol */
}
.loan-calc-button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: var(–primary-blue);
color: var(–white);
border: none;
border-radius: 5px;
font-size: 18px;
font-weight: 500;
cursor: pointer;
transition: background-color 0.3s ease;
margin-top: 20px;
}
.loan-calc-button:hover {
background-color: #003b7d;
}
.result-section {
flex: 1;
min-width: 280px;
background-color: var(–light-background);
padding: 25px;
border-radius: 6px;
border: 1px solid var(–border-color);
}
.result-section h2 {
margin-top: 0;
margin-bottom: 20px;
color: var(–primary-blue);
font-size: 22px;
text-align: center;
}
.result-summary {
background-color: var(–white);
padding: 15px;
border-radius: 5px;
border: 1px solid var(–border-color);
margin-bottom: 20px;
}
.result-summary p {
margin: 8px 0;
font-size: 15px;
display: flex;
justify-content: space-between;
}
.result-summary p strong {
color: var(–gray-text);
}
.result-summary .total-payment {
font-size: 18px;
font-weight: bold;
color: var(–success-green);
margin-top: 10px;
}
.schedule-table-container {
margin-top: 30px;
overflow-x: auto;
}
.schedule-table {
width: 100%;
border-collapse: collapse;
margin-top: 10px;
}
.schedule-table th,
.schedule-table td {
border: 1px solid var(–border-color);
padding: 10px;
text-align: right;
font-size: 14px;
}
.schedule-table th {
background-color: var(–primary-blue);
color: var(–white);
font-weight: 500;
position: sticky;
top: 0; /* Sticky header */
}
.schedule-table td {
background-color: var(–white);
}
.schedule-table tbody tr:nth-child(even) td {
background-color: var(–light-background);
}
.article-section {
padding: 30px;
margin-top: 20px;
background-color: var(–white);
border-radius: 8px;
box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
}
.article-section h2 {
color: var(–primary-blue);
border-bottom: 2px solid var(–primary-blue);
padding-bottom: 10px;
margin-bottom: 20px;
font-size: 26px;
}
.article-section h3 {
color: var(–primary-blue);
margin-top: 25px;
margin-bottom: 15px;
font-size: 20px;
}
.article-section p {
margin-bottom: 15px;
}
.article-section ul {
margin-left: 20px;
margin-bottom: 15px;
}
.article-section li {
margin-bottom: 8px;
}
.error-message {
color: red;
text-align: center;
margin-top: 15px;
font-weight: bold;
}
@media (max-width: 768px) {
.calculator-body {
flex-direction: column;
}
.input-section, .result-section {
flex: none;
width: 100%;
}
.schedule-table th, .schedule-table td {
font-size: 12px;
padding: 8px;
}
}
Payment Schedule Summary
Monthly Payment: $0.00
Total Interest Paid: $0.00
Total Principal Paid: $0.00
Total Amount Paid: $0.00
Amortization Schedule
| Payment # |
Payment Date |
Payment Amount |
Principal Paid |
Interest Paid |
Remaining Balance |
Understanding Amortization Schedules
An amortization schedule is a table that shows how a loan or mortgage will be paid off over time. It details each periodic payment, breaking it down into the portion that goes towards the principal balance and the portion that covers the interest owed. This schedule is crucial for borrowers to understand the true cost of their loan and how their payments affect the outstanding balance.
How Amortization Works
Amortization is the process of paying off a debt over time through regular payments. For loans like mortgages, auto loans, or personal loans, each payment consists of two parts:
- Principal: The original amount of money borrowed.
- Interest: The cost of borrowing money, calculated as a percentage of the outstanding principal.
In an amortizing loan, the payment amount remains constant over the loan's term. However, the distribution between principal and interest changes with each payment. Early payments are heavily weighted towards interest, while later payments focus more on reducing the principal.
The Math Behind the Monthly Payment
The most common formula used to calculate the fixed periodic payment (M) for an amortizing loan is the annuity formula:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
- M = Periodic Payment (the amount you'll pay each period)
- P = Principal Loan Amount (the total amount borrowed)
- i = Periodic Interest Rate (annual interest rate divided by the number of payment periods per year)
- n = Total Number of Payments (loan term in years multiplied by the number of payment periods per year)
Calculating the Amortization Schedule
Once the periodic payment (M) is determined, the schedule is built step-by-step:
- Calculate Interest Paid for the Period: Interest = Remaining Balance * Periodic Interest Rate (i)
- Calculate Principal Paid for the Period: Principal = Periodic Payment (M) – Interest Paid
- Calculate New Remaining Balance: New Balance = Previous Balance – Principal Paid
- Repeat: Use the new remaining balance for the next period's calculations.
This process continues until the remaining balance reaches zero (or very close to it due to rounding).
Use Cases for an Amortization Calculator
- Mortgage Planning: Understand how much your monthly mortgage payment will be, including interest, and how quickly you can build equity.
- Loan Comparisons: Compare different loan offers with varying interest rates and terms to see the total cost over time.
- Financial Budgeting: Accurately budget for loan payments and predict future outstanding balances.
- Extra Payments: Simulate the impact of making extra payments to pay off the loan faster and save on interest.
- Debt Management: Visualize the payoff journey for various types of loans, such as auto loans or student loans.
Using an amortization schedule calculator helps demystify loan payments, empowering borrowers to make informed financial decisions.
function formatCurrency(amount) {
return "$" + amount.toFixed(2).replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}
function formatInterest(rate) {
return rate.toFixed(3) + "%";
}
function formatNumber(num) {
return num.toFixed(2).replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}
function calculateAmortization() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var loanTermYears = parseFloat(document.getElementById("loanTermYears").value);
var paymentFrequency = parseInt(document.getElementById("paymentFrequency").value);
var errorMessageDiv = document.getElementById("errorMessage");
errorMessageDiv.textContent = ""; // Clear previous errors
if (isNaN(loanAmount) || loanAmount <= 0) {
errorMessageDiv.textContent = "Please enter a valid loan amount greater than zero.";
return;
}
if (isNaN(annualInterestRate) || annualInterestRate < 0) {
errorMessageDiv.textContent = "Please enter a valid annual interest rate (0% or greater).";
return;
}
if (isNaN(loanTermYears) || loanTermYears <= 0) {
errorMessageDiv.textContent = "Please enter a valid loan term in years greater than zero.";
return;
}
if (isNaN(paymentFrequency) || paymentFrequency 0) {
monthlyPayment = loanAmount * (periodicInterestRate * Math.pow(1 + periodicInterestRate, numberOfPayments)) / (Math.pow(1 + periodicInterestRate, numberOfPayments) – 1);
} else {
// If interest rate is 0, payment is just principal divided by number of payments
monthlyPayment = loanAmount / numberOfPayments;
}
// Round to 2 decimal places for currency
monthlyPayment = parseFloat(monthlyPayment.toFixed(2));
var totalInterestPaid = 0;
var totalPrincipalPaid = 0;
var remainingBalance = loanAmount;
var amortizationSchedule = [];
var currentDate = new Date(); // Start date for payments
for (var i = 1; i monthlyPayment && i > 1) {
principalForPeriod = monthlyPayment – interestForPeriod;
}
// Ensure balance becomes exactly zero
if (remainingBalance remainingBalance) {
principalForPeriod = remainingBalance;
monthlyPayment = principalForPeriod + interestForPeriod; // Adjust payment if principal exceeds balance
}
// Ensure remaining balance doesn't go negative
remainingBalance -= principalForPeriod;
if (remainingBalance < 0) {
remainingBalance = 0;
}
totalInterestPaid += interestForPeriod;
totalPrincipalPaid += principalForPeriod;
// Calculate payment date (simplified – assumes consistent frequency from start date)
var paymentDate = new Date(currentDate);
switch(paymentFrequency) {
case 12: // Monthly
paymentDate.setMonth(currentDate.getMonth() + i);
break;
case 24: // Bi-monthly (assuming every 2 weeks roughly)
paymentDate.setDate(currentDate.getDate() + (i * 14));
break;
case 26: // Bi-weekly (every 14 days)
paymentDate.setDate(currentDate.getDate() + (i * 14));
break;
case 52: // Weekly
paymentDate.setDate(currentDate.getDate() + (i * 7));
break;
case 1: // Annually
paymentDate.setFullYear(currentDate.getFullYear() + i);
break;
default: // Default to monthly if frequency is unusual or not specified
paymentDate.setMonth(currentDate.getMonth() + i);
break;
}
amortizationSchedule.push({
paymentNum: i,
paymentDate: paymentDate.toLocaleDateString(),
paymentAmount: monthlyPayment,
principalPaid: principalForPeriod,
interestPaid: interestForPeriod,
remainingBalance: remainingBalance
});
}
// Correcting potential floating point inaccuracies for totals
totalInterestPaid = parseFloat(totalInterestPaid.toFixed(2));
totalPrincipalPaid = parseFloat(totalPrincipalPaid.toFixed(2));
var totalAmountPaid = totalPrincipalPaid + totalInterestPaid;
document.getElementById("monthlyPayment").textContent = formatCurrency(monthlyPayment);
document.getElementById("totalInterest").textContent = formatCurrency(totalInterestPaid);
document.getElementById("totalPrincipal").textContent = formatCurrency(totalPrincipalPaid);
document.getElementById("totalAmountPaid").textContent = formatCurrency(totalAmountPaid);
var scheduleBody = document.getElementById("amortizationScheduleBody");
scheduleBody.innerHTML = ""; // Clear previous schedule
amortizationSchedule.forEach(function(payment) {
var row = scheduleBody.insertRow();
row.insertCell().textContent = payment.paymentNum;
row.insertCell().textContent = payment.paymentDate;
row.insertCell().textContent = formatCurrency(payment.paymentAmount);
row.insertCell().textContent = formatCurrency(payment.principalPaid);
row.insertCell().textContent = formatCurrency(payment.interestPaid);
row.insertCell().textContent = formatCurrency(payment.remainingBalance);
});
}
// Optional: Trigger calculation on page load if fields have default values
// window.onload = calculateAmortization;