Amortization Schedule Calculator
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Amortization Schedule Calculator
Loan Amount ($):
Annual Interest Rate (%):
Loan Term (Years):
Payment Frequency:
Monthly (12)
Bi-Monthly (24)
Weekly (52)
Annually (1)
Calculate Amortization Schedule
Total Paid: $0.00
Amortization Schedule
Payment #
Payment Date
Beginning Balance
Payment
Interest Paid
Principal Paid
Ending Balance
Understanding Amortization Schedules
An amortization schedule is a table that details each periodic payment on an amortizing loan. An amortizing loan is one where each payment consists of both interest and principal, gradually reducing the loan balance over time until it reaches zero at the end of the loan term. This is the standard method for calculating payments on mortgages, auto loans, personal loans, and many other types of debt.
How the Calculation Works
The core of an amortization schedule is calculating the fixed periodic payment and then breaking down each payment into its interest and principal components. Here's a breakdown of the formulas used:
1. Monthly Interest Rate
The first step is to convert the annual interest rate into a periodic interest rate. If payments are made monthly, the annual rate is divided by 12.
Periodic Interest Rate (r) = Annual Interest Rate / Number of Payments Per Year
2. Total Number of Payments
This is the total number of payments that will be made over the life of the loan.
Total Number of Payments (n) = Loan Term (in Years) * Number of Payments Per Year
3. Calculating the Periodic Payment (P)
The most common formula used to calculate the fixed periodic payment is the annuity formula:
P = [ L * r * (1 + r)^n ] / [ (1 + r)^n – 1]
Where:
P = Periodic PaymentL = Loan Amount (Principal)r = Periodic Interest Rate (from step 1)n = Total Number of Payments (from step 2)
4. Amortization Breakdown for Each Payment
For each payment period, the breakdown is as follows:
Interest Paid = Beginning Balance * Periodic Interest Rate (r)Principal Paid = Periodic Payment (P) – Interest PaidEnding Balance = Beginning Balance – Principal Paid
The Ending Balance of one period becomes the Beginning Balance of the next period. This process repeats until the Ending Balance reaches zero.
Why Use an Amortization Schedule?
Debt Management: Helps borrowers understand how their payments are applied and how much interest they are paying over time.Financial Planning: Essential for budgeting and understanding the total cost of borrowing.Loan Comparison: Allows for easy comparison of different loan offers by showing total interest paid and the payment structure.Tax Purposes: In some cases, the interest paid can be tax-deductible, and the schedule provides the necessary documentation.
This calculator provides a clear view of your loan's repayment journey, helping you make informed financial decisions.
function calculateAmortization() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var loanTerm = parseInt(document.getElementById("loanTerm").value);
var paymentFrequency = parseInt(document.getElementById("paymentFrequency").value);
var resultDiv = document.getElementById("result");
var tableBody = document.getElementById("amortizationTable").getElementsByTagName('tbody')[0];
var tableContainer = document.getElementById("amortizationTableContainer");
// Clear previous results and table
resultDiv.innerHTML = 'Total Paid: $0.00Total Interest Paid: $0.00';
tableBody.innerHTML = ";
tableContainer.style.display = 'none';
// Input validation
if (isNaN(loanAmount) || loanAmount <= 0) {
resultDiv.innerHTML = "Please enter a valid loan amount.";
return;
}
if (isNaN(annualInterestRate) || annualInterestRate < 0) {
resultDiv.innerHTML = "Please enter a valid annual interest rate.";
return;
}
if (isNaN(loanTerm) || loanTerm <= 0) {
resultDiv.innerHTML = "Please enter a valid loan term in years.";
return;
}
if (isNaN(paymentFrequency) || paymentFrequency <= 0) {
resultDiv.innerHTML = "Please select a valid payment frequency.";
return;
}
var periodicInterestRate = annualInterestRate / 100 / paymentFrequency;
var numberOfPayments = loanTerm * paymentFrequency;
// Calculate periodic payment
var periodicPayment;
if (periodicInterestRate === 0) {
periodicPayment = loanAmount / numberOfPayments;
} else {
periodicPayment = (loanAmount * periodicInterestRate * Math.pow(1 + periodicInterestRate, numberOfPayments)) / (Math.pow(1 + periodicInterestRate, numberOfPayments) – 1);
}
// Handle cases where periodicPayment might be extremely small or NaN due to inputs
if (isNaN(periodicPayment) || periodicPayment <= 0) {
resultDiv.innerHTML = "Calculation error. Please check your inputs.";
return;
}
var totalInterestPaid = 0;
var beginningBalance = loanAmount;
var currentDate = new Date(); // Use current date as a starting point for payment dates
for (var i = 0; i beginningBalance) {
principalPaid = beginningBalance;
periodicPayment = interestPaid + principalPaid;
}
var endingBalance = beginningBalance – principalPaid;
// Rounding to avoid floating point inaccuracies causing issues with ending balance
interestPaid = Math.round(interestPaid * 100) / 100;
principalPaid = Math.round(principalPaid * 100) / 100;
periodicPayment = Math.round(periodicPayment * 100) / 100;
endingBalance = Math.round(endingBalance * 100) / 100;
totalInterestPaid += interestPaid;
beginningBalance = endingBalance;
// Add row to table
var row = tableBody.insertRow();
var cell1 = row.insertCell(0); // Payment #
var cell2 = row.insertCell(1); // Payment Date
var cell3 = row.insertCell(2); // Beginning Balance
var cell4 = row.insertCell(3); // Payment
var cell5 = row.insertCell(4); // Interest Paid
var cell6 = row.insertCell(5); // Principal Paid
var cell7 = row.insertCell(6); // Ending Balance
cell1.textContent = (i + 1);
// Format date – adding one period
currentDate.setMonth(currentDate.getMonth() + 1); // Increment month
cell2.textContent = currentDate.toLocaleDateString();
cell3.textContent = formatCurrency(loanAmount – principalPaid – totalInterestPaid + interestPaid); // Beginning balance of this payment
cell4.textContent = formatCurrency(periodicPayment);
cell5.textContent = formatCurrency(interestPaid);
cell6.textContent = formatCurrency(principalPaid);
cell7.textContent = formatCurrency(endingBalance < 0 ? 0 : endingBalance); // Ensure ending balance is not negative
// Update total interest and beginning balance for the next iteration if we are adjusting the last payment
if (endingBalance < 0.01 && i 0) {
periodicPayment = (loanAmount * periodicInterestRate) / (1 – Math.pow(1 + periodicInterestRate, -remainingPayments));
} else {
periodicPayment = (loanAmount) / remainingPayments;
}
principalPaid = periodicPayment – (endingBalance * periodicInterestRate);
periodicPayment = Math.round(periodicPayment * 100) / 100;
}
beginningBalance = endingBalance < 0 ? 0 : endingBalance; // Set balance for next iteration
}
var totalPaid = periodicPayment * numberOfPayments;
totalInterestPaid = Math.round(totalInterestPaid * 100) / 100; // Final rounding
resultDiv.innerHTML = 'Total Paid: ' + formatCurrency(totalPaid) + 'Total Interest Paid: ' + formatCurrency(totalInterestPaid);
tableContainer.style.display = 'block';
}
function formatCurrency(amount) {
return '$' + parseFloat(amount).toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}