Mortgage Calculator Prepayment

:root {
–primary-color: #004a99;
–success-color: #28a745;
–background-color: #f8f9fa;
–text-color: #333;
–border-color: #ddd;
–card-background: #fff;
–shadow: 0 2px 5px rgba(0,0,0,0.1);
}
body {
font-family: ‘Segoe UI’, Tahoma, Geneva, Verdana, sans-serif;
background-color: var(–background-color);
color: var(–text-color);
line-height: 1.6;
margin: 0;
padding: 0;
}
.container {
max-width: 1000px;
margin: 20px auto;
padding: 20px;
background-color: var(–card-background);
border-radius: 8px;
box-shadow: var(–shadow);
}
h1, h2, h3 {
color: var(–primary-color);
text-align: center;
}
h1 {
margin-bottom: 10px;
}
h2 {
margin-top: 30px;
margin-bottom: 15px;
border-bottom: 2px solid var(–primary-color);
padding-bottom: 5px;
}
.loan-calc-container {
background-color: var(–card-background);
padding: 25px;
border-radius: 8px;
box-shadow: var(–shadow);
margin-bottom: 30px;
}
.input-group {
margin-bottom: 15px;
display: flex;
flex-direction: column;
}
.input-group label {
display: block;
margin-bottom: 8px;
font-weight: bold;
color: var(–primary-color);
}
.input-group input[type=”number”],
.input-group input[type=”text”],
.input-group select {
width: calc(100% – 20px);
padding: 10px;
border: 1px solid var(–border-color);
border-radius: 4px;
font-size: 1rem;
box-sizing: border-box;
}
.input-group input[type=”number”]:focus,
.input-group input[type=”text”]:focus,
.input-group select:focus {
outline: none;
border-color: var(–primary-color);
box-shadow: 0 0 0 2px rgba(0, 74, 153, 0.2);
}
.input-group .helper-text {
font-size: 0.85rem;
color: #666;
margin-top: 5px;
}
.input-group .error-message {
color: red;
font-size: 0.8rem;
margin-top: 5px;
display: none; /* Hidden by default */
}
.button-group {
display: flex;
justify-content: space-between;
margin-top: 20px;
flex-wrap: wrap;
gap: 10px;
}
.button-group button {
padding: 10px 20px;
border: none;
border-radius: 4px;
cursor: pointer;
font-size: 1rem;
font-weight: bold;
transition: background-color 0.3s ease;
flex: 1;
min-width: 150px;
}
.btn-calculate {
background-color: var(–primary-color);
color: white;
}
.btn-calculate:hover {
background-color: #003366;
}
.btn-reset {
background-color: #6c757d;
color: white;
}
.btn-reset:hover {
background-color: #5a6268;
}
.btn-copy {
background-color: #17a2b8;
color: white;
}
.btn-copy:hover {
background-color: #117a8b;
}
#results {
margin-top: 30px;
padding: 20px;
background-color: var(–primary-color);
color: white;
border-radius: 8px;
text-align: center;
box-shadow: var(–shadow);
}
#results h3 {
color: white;
margin-top: 0;
margin-bottom: 15px;
}
.primary-result {
font-size: 2.5rem;
font-weight: bold;
margin-bottom: 10px;
}
.intermediate-results div {
margin-bottom: 8px;
font-size: 1.1rem;
}
.intermediate-results span {
font-weight: bold;
}
.formula-explanation {
font-size: 0.9rem;
margin-top: 15px;
opacity: 0.8;
}
table {
width: 100%;
border-collapse: collapse;
margin-top: 20px;
box-shadow: var(–shadow);
overflow-x: auto; /* Make table scrollable */
display: block; /* Needed for overflow-x */
white-space: nowrap; /* Prevent wrapping */
}
th, td {
padding: 12px 15px;
text-align: left;
border: 1px solid var(–border-color);
}
thead {
background-color: var(–primary-color);
color: white;
}
tbody tr:nth-child(even) {
background-color: #f2f2f2;
}
tbody tr:hover {
background-color: #e9ecef;
}
caption {
font-size: 1.1rem;
font-weight: bold;
color: var(–primary-color);
margin-bottom: 10px;
text-align: left;
}
canvas {
max-width: 100%;
height: auto;
display: block;
margin: 20px auto;
border: 1px solid var(–border-color);
border-radius: 4px;
}
.article-content {
margin-top: 40px;
background-color: var(–card-background);
padding: 30px;
border-radius: 8px;
box-shadow: var(–shadow);
}
.article-content h2 {
text-align: left;
border-bottom: 1px solid var(–border-color);
padding-bottom: 8px;
margin-top: 25px;
}
.article-content h3 {
text-align: left;
margin-top: 20px;
margin-bottom: 10px;
color: var(–primary-color);
}
.article-content p, .article-content ul, .article-content ol {
margin-bottom: 15px;
}
.article-content ul, .article-content ol {
padding-left: 20px;
}
.article-content li {
margin-bottom: 8px;
}
.faq-item {
margin-bottom: 15px;
padding: 10px;
border: 1px solid var(–border-color);
border-radius: 4px;
background-color: #fdfdfd;
}
.faq-item strong {
color: var(–primary-color);
cursor: pointer;
display: block;
margin-bottom: 5px;
}
.faq-item p {
margin-bottom: 0;
display: none; /* Hidden by default */
}
.internal-links ul {
list-style: none;
padding: 0;
}
.internal-links li {
margin-bottom: 10px;
}
.internal-links a {
color: var(–primary-color);
text-decoration: none;
font-weight: bold;
}
.internal-links a:hover {
text-decoration: underline;
}
.internal-links span {
font-size: 0.9rem;
color: #555;
display: block;
margin-top: 3px;
}
.highlight {
background-color: var(–success-color);
color: white;
padding: 2px 5px;
border-radius: 3px;
}
.loan-calc-container .button-group {
justify-content: center;
gap: 15px;
}
.loan-calc-container .button-group button {
flex: unset;
width: auto;
}
@media (max-width: 768px) {
.container {
margin: 10px;
padding: 15px;
}
.button-group {
flex-direction: column;
align-items: center;
}
.button-group button {
width: 100%;
max-width: 300px;
}
h1 {
font-size: 1.8rem;
}
h2 {
font-size: 1.5rem;
}
.primary-result {
font-size: 2rem;
}
table {
font-size: 0.9rem;
}
th, td {
padding: 10px 12px;
}
}

Understand the power of extra mortgage payments and how they can save you thousands in interest and shorten your loan term.

Mortgage Prepayment Calculator

Amortization Schedule Comparison

Payment #	Date	Starting Balance	Payment	Principal	Interest	Ending Balance

What is Mortgage Prepayment?

Mortgage prepayment refers to the act of paying down your mortgage loan balance faster than your scheduled payments require. This can be done through various methods, such as making larger monthly payments, making lump-sum payments, or making more frequent payments (like paying bi-weekly instead of monthly). The primary goal of mortgage prepayment is to reduce the total amount of interest paid over the life of the loan and to pay off the mortgage sooner. Many homeowners choose to prepay their mortgages to gain financial freedom, reduce debt, or free up cash flow for other investments or life events. Understanding how mortgage prepayment works is crucial for effective financial planning.

Who should use mortgage prepayment strategies?

• Homeowners who have extra disposable income and want to save on interest.
• Individuals looking to pay off their mortgage before retirement.
• Those who want to reduce their debt burden and improve their financial standing.
• People who want to build equity faster in their homes.

Common misconceptions about mortgage prepayment include:

• Thinking it’s always financially beneficial without considering opportunity costs (e.g., investing elsewhere).
• Believing that all extra payments automatically go towards the principal (some lenders might apply them to future interest or payments first).
• Underestimating the power of even small, consistent extra payments over time.

Mortgage Prepayment Formula and Mathematical Explanation

The core of mortgage prepayment analysis involves understanding how extra payments affect the loan’s amortization schedule. While a standard mortgage payment covers interest accrued for the period and a portion of the principal, any amount paid above the scheduled payment is typically applied directly to the principal balance. This reduction in principal has a compounding effect, as future interest is calculated on a smaller balance.

The monthly interest paid is calculated as: Interest = Remaining Balance * (Annual Interest Rate / 12)

The principal portion of a standard payment is: Principal = Scheduled Payment - Interest

When an extra payment is made, it’s added to the principal portion:

Total Principal Paid = Scheduled Principal + Extra Payment

New Remaining Balance = Old Remaining Balance - Total Principal Paid

The total number of payments and total interest paid are then recalculated based on this new, lower balance and the original interest rate.

Variables Table

Variable	Meaning	Unit	Typical Range
P	Original Loan Amount	$	$50,000 – $1,000,000+
r	Annual Interest Rate	%	2% – 10%+
n	Original Loan Term	Years	15, 30
M	Monthly Payment	$	Calculated
E	Monthly Extra Payment	$	$0 – $1,000+
Ppaid	Total Principal Paid	$	Calculated
Ipaid	Total Interest Paid	$	Calculated
Nnew	New Loan Term	Years	Calculated

Practical Examples (Real-World Use Cases)

Example 1: Aggressive Prepayment

Sarah has a mortgage with the following details:

• Original Loan Amount: $300,000
• Annual Interest Rate: 4.5%
• Original Loan Term: 30 years
• Standard Monthly Payment: $1,520.06

Sarah decides to make an extra $300 payment towards her principal each month. Using the mortgage prepayment calculator:

• Inputs: Loan Amount: $300,000, Interest Rate: 4.5%, Term: 30 years, Extra Monthly Payment: $300
• Results:
  • Total Interest Saved: Approximately $105,000
  • New Loan Term: Approximately 22 years (saving 8 years)
  • Total Interest Paid: Approximately $215,000
  • Total Payments Made: Approximately 264

Interpretation: By consistently paying an extra $300 per month, Sarah will save over $105,000 in interest and pay off her mortgage 8 years earlier. This demonstrates the significant impact of disciplined prepayment.

Example 2: Bi-weekly Payment Strategy

John and Lisa have a mortgage with:

• Original Loan Amount: $400,000
• Annual Interest Rate: 5.0%
• Original Loan Term: 30 years
• Standard Monthly Payment: $2,147.37

They decide to switch to a bi-weekly payment plan, paying half of their monthly payment every two weeks. This results in one extra monthly payment per year.

• Inputs: Loan Amount: $400,000, Interest Rate: 5.0%, Term: 30 years, Payment Frequency: Bi-weekly (effectively adding ~$179 per month on average)
• Results:
  • Total Interest Saved: Approximately $75,000
  • New Loan Term: Approximately 25 years (saving 5 years)
  • Total Interest Paid: Approximately $375,000
  • Total Payments Made: Approximately 300 (equivalent to 25 years)

Interpretation: The bi-weekly payment strategy, which equates to making one extra monthly payment annually, allows John and Lisa to shave 5 years off their mortgage and save a substantial amount in interest, illustrating how optimizing payment frequency can accelerate payoff.

How to Use This Mortgage Prepayment Calculator

Using our mortgage prepayment calculator is straightforward. Follow these steps to understand the potential savings and benefits of making extra payments on your mortgage:

1. Enter Original Loan Details: Input your current mortgage’s original loan amount, annual interest rate, and the original loan term in years.
2. Specify Extra Payment: Enter the amount you plan to pay in addition to your regular monthly mortgage payment. This could be a fixed amount or zero if you’re just exploring standard amortization.
3. Select Payment Frequency: Choose your regular payment frequency (e.g., Monthly, Bi-weekly). This helps accurately calculate the total number of payments and the impact of strategies like the “13th payment” per year.
4. Click Calculate: Press the “Calculate” button. The calculator will process your inputs and display the results.

How to Read Results:

• Primary Highlighted Result (Total Interest Saved): This is the most significant figure, showing the total dollar amount you can save on interest over the life of the loan by making the specified extra payments. A higher number indicates greater savings.
• New Loan Term: This shows how much sooner you will pay off your mortgage in years and months. A shorter term means faster debt freedom.
• Total Interest Paid: This is the total interest you will pay with the extra payments, compared to the total interest without them (which you can infer from the savings).
• Total Payments Made: This indicates the total number of payments you will make until the loan is fully paid off.
• Amortization Table & Chart: These provide a detailed breakdown of how each payment is applied (principal vs. interest) and visualize the accelerated principal reduction and interest savings over time.

Decision-Making Guidance:

The results from this mortgage prepayment calculator can help you make informed decisions. If the potential interest savings and shortened loan term align with your financial goals, consider implementing a consistent prepayment strategy. Evaluate your budget to determine a realistic extra payment amount. Remember to ensure your lender applies extra payments directly to the principal to maximize benefits. If you have high-interest debt elsewhere or potential investment opportunities with higher guaranteed returns, weigh those options against the guaranteed savings from mortgage prepayment.

Key Factors That Affect Mortgage Prepayment Results

Several factors significantly influence the effectiveness and impact of mortgage prepayment strategies. Understanding these can help you tailor your approach for maximum benefit:

1. Interest Rate: This is arguably the most critical factor. Higher interest rates mean more of your regular payment goes towards interest, making prepayments more impactful. Paying down a high-interest loan offers a guaranteed return equal to the interest rate, which is often higher than what can be safely earned through other investments.
2. Time Remaining on Loan: Prepayments made earlier in the loan term have a much greater effect. This is because early payments are heavily weighted towards interest. Reducing the principal early on significantly cuts down the base on which future interest is calculated, leading to substantial long-term savings.
3. Amount of Extra Payments: The more you can afford to pay extra, the faster your loan will be paid off and the more interest you will save. Even small, consistent extra payments can make a difference over time, but larger, irregular lump sums can dramatically accelerate the process.
4. Loan Term: Shorter loan terms (e.g., 15-year vs. 30-year) naturally have less interest paid overall. When prepaying on a longer-term loan, the potential for shortening the term and reducing interest is much higher compared to a loan already nearing its end.
5. Payment Frequency: Switching to bi-weekly payments (paying half the monthly amount every two weeks) results in one extra monthly payment per year. This strategy effectively accelerates principal reduction without a significant strain on monthly cash flow.
6. Inflation and Opportunity Cost: While prepaying a mortgage offers a guaranteed “return” (interest saved), it ties up cash that could potentially be invested elsewhere. If inflation is high or you have investment opportunities with significantly higher expected returns (after considering risk), it might be more financially advantageous to invest rather than prepay. This is a crucial consideration for maximizing wealth.
7. Lender Policies and Fees: Some mortgages have prepayment penalties, especially early in the loan term or for certain types of loans (like some government-backed loans). Always check your mortgage agreement for any such fees. Ensure your lender applies extra payments directly to the principal; otherwise, they might be applied to future interest or payments, negating the benefit.

Frequently Asked Questions (FAQ)

What is the best way to make extra mortgage payments?

The most effective way is to ensure your extra payments are applied directly to the principal balance. You can often specify this with your lender, either by writing “principal only” on your check memo or by adjusting settings in your online payment portal. Making lump-sum payments or increasing your regular monthly payment are common methods.

Are there any risks to prepaying my mortgage?

The main “risk” is opportunity cost. The money used for prepayment cannot be used for other investments that might yield higher returns, or for emergencies. Also, ensure your loan doesn’t have prepayment penalties. Once paid, the principal cannot be accessed without refinancing or a home equity loan.

Should I prioritize prepaying my mortgage or investing?

This depends on your risk tolerance, expected investment returns, and the mortgage interest rate. If your mortgage rate is high (e.g., >6-7%), prepaying offers a guaranteed return equal to that rate. If you can consistently earn significantly more than your mortgage rate in the stock market (after taxes and fees), investing might be more lucrative, though riskier. Many people choose a balanced approach.

What happens if I miss a payment after making extra ones?

Making extra payments does not excuse you from your regularly scheduled payments. If you miss a payment, you will still incur late fees and potential negative impacts on your credit score, regardless of how much extra principal you’ve paid. Ensure your regular payment is always made on time.

Does prepaying affect my tax deductions?

Yes, since you’ll be paying less total interest over the life of the loan, your deductible mortgage interest expense will decrease each year. This could potentially reduce your tax benefit from homeownership, although the overall financial gain from saving interest usually outweighs this.

Can I get my extra payments back if I need the money later?

Generally, no. Once you pay down principal, that money is considered part of your equity. To access it, you would typically need to refinance your mortgage or take out a home equity loan or line of credit, which involves new fees and potentially a different interest rate.

How does a bi-weekly payment plan work?

A true bi-weekly plan involves paying half of your monthly mortgage payment every two weeks. Since there are 52 weeks in a year, this results in 26 half-payments, which equals 13 full monthly payments (instead of 12). This extra payment goes directly towards principal, accelerating payoff.

What if my lender doesn’t allow extra principal payments?

This is rare for most standard mortgages, but if it occurs, you should consult your loan documents or contact your lender directly. Some lenders might automatically apply extra funds to future payments rather than principal. If this is the case, you might need to explore other options or consider refinancing to a loan that allows principal prepayments without penalty.

var chartInstance = null; // Global variable to hold chart instance

function formatCurrency(amount) {
return “$” + amount.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, ‘$&,’);
}

function formatNumber(num) {
return num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, ‘$&,’);
}

function calculateMonthlyPayment(principal, annualRate, termInYears) {
var monthlyRate = annualRate / 100 / 12;
var numberOfMonths = termInYears * 12;
if (monthlyRate === 0) return principal / numberOfMonths;
var payment = principal * monthlyRate / (1 – Math.pow(1 + monthlyRate, -numberOfMonths));
return isNaN(payment) ? 0 : payment;
}

function validateInput(id, min, max, errorMessageId, allowEmpty = false) {
var input = document.getElementById(id);
var value = parseFloat(input.value);
var errorDiv = document.getElementById(errorMessageId);
errorDiv.style.display = ‘none’; // Hide error by default

if (!allowEmpty && (input.value === “” || isNaN(value))) {
errorDiv.textContent = “This field is required.”;
errorDiv.style.display = ‘block’;
return false;
}
if (input.value !== “” && isNaN(value)) {
errorDiv.textContent = “Please enter a valid number.”;
errorDiv.style.display = ‘block’;
return false;
}
if (value max) {
errorDiv.textContent = “Value is too high.”;
errorDiv.style.display = ‘block’;
return false;
}
return true;
}

function calculateMortgagePrepayment() {
// Clear previous errors
document.getElementById(‘loanAmountError’).style.display = ‘none’;
document.getElementById(‘interestRateError’).style.display = ‘none’;
document.getElementById(‘loanTermError’).style.display = ‘none’;
document.getElementById(‘extraPaymentError’).style.display = ‘none’;

// Validate inputs
var isValid = true;
isValid &= validateInput(‘loanAmount’, 0, undefined, ‘loanAmountError’);
isValid &= validateInput(‘interestRate’, 0, 100, ‘interestRateError’);
isValid &= validateInput(‘loanTerm’, 1, undefined, ‘loanTermError’);
isValid &= validateInput(‘extraPayment’, 0, undefined, ‘extraPaymentError’);

if (!isValid) {
document.getElementById(‘results’).style.display = ‘none’;
return;
}

var loanAmount = parseFloat(document.getElementById(‘loanAmount’).value);
var annualInterestRate = parseFloat(document.getElementById(‘interestRate’).value);
var loanTermYears = parseInt(document.getElementById(‘loanTerm’).value);
var extraMonthlyPayment = parseFloat(document.getElementById(‘extraPayment’).value);
var paymentFrequency = parseInt(document.getElementById(‘paymentFrequency’).value);

var monthlyInterestRate = annualInterestRate / 100 / 12;
var numberOfMonths = loanTermYears * 12;

// Calculate standard monthly payment
var standardMonthlyPayment = calculateMonthlyPayment(loanAmount, annualInterestRate, loanTermYears);

// Calculate total payments and interest without prepayment
var totalInterestWithoutPrepayment = (standardMonthlyPayment * numberOfMonths) – loanAmount;

// — Calculate with prepayment —
var currentBalance = loanAmount;
var totalPaid = 0;
var totalInterestPaid = 0;
var totalPrincipalPaid = 0;
var months = 0;
var amortizationData = [];
var currentDate = new Date(); // Start date for amortization schedule

// Adjust payment based on frequency
var effectiveMonthlyPayment = standardMonthlyPayment + extraMonthlyPayment;
var actualPaymentAmount = effectiveMonthlyPayment;

// Handle bi-weekly/semi-monthly logic for total payments per year
var paymentsPerYear = paymentFrequency;
var effectiveExtraPaymentPerMonth = extraMonthlyPayment;
if (paymentFrequency === 26) { // Bi-weekly
effectiveExtraPaymentPerMonth = (standardMonthlyPayment / 2) * (26 / 12) – (standardMonthlyPayment / 2);
actualPaymentAmount = standardMonthlyPayment / 2; // This is the base payment amount
} else if (paymentFrequency === 24) { // Semi-monthly
effectiveExtraPaymentPerMonth = (standardMonthlyPayment / 2) * (24 / 12) – (standardMonthlyPayment / 2);
actualPaymentAmount = standardMonthlyPayment / 2; // This is the base payment amount
} else { // Monthly
actualPaymentAmount = standardMonthlyPayment;
}

// Recalculate effective monthly payment considering frequency
var totalMonthlyPayment = standardMonthlyPayment + extraMonthlyPayment;

while (currentBalance > 0.01) { // Continue as long as there’s a balance
months++;
var interestForMonth = currentBalance * monthlyInterestRate;
var principalForMonth = 0;

// Determine how much of the payment goes to principal
var paymentToApply = totalMonthlyPayment;
if (paymentFrequency === 26) { // Bi-weekly
paymentToApply = actualPaymentAmount + (extraMonthlyPayment / (26/12)); // Distribute extra payment
} else if (paymentFrequency === 24) { // Semi-monthly
paymentToApply = actualPaymentAmount + (extraMonthlyPayment / (24/12)); // Distribute extra payment
}

// Ensure payment doesn’t exceed remaining balance + interest
if (paymentToApply > currentBalance + interestForMonth) {
paymentToApply = currentBalance + interestForMonth;
}

principalForMonth = paymentToApply – interestForMonth;

// Ensure principal doesn’t make balance negative
if (principalForMonth > currentBalance) {
principalForMonth = currentBalance;
paymentToApply = currentBalance + interestForMonth; // Adjust payment if principal covers remaining balance
}

currentBalance -= principalForMonth;
totalInterestPaid += interestForMonth;
totalPrincipalPaid += principalForMonth;
totalPaid += paymentToApply;

// Store amortization data
var paymentDate = new Date(currentDate);
paymentDate.setMonth(currentDate.getMonth() + months -1); // Adjust month for display

amortizationData.push({
paymentNum: months,
date: paymentDate.toLocaleDateString(),
startBalance: currentBalance + principalForMonth, // Balance before this payment
payment: paymentToApply,
principal: principalForMonth,
interest: interestForMonth,
endBalance: currentBalance
});

// Prevent infinite loops for edge cases
if (months > loanTermYears * 12 * 5) { // Safety break after 5x original term
console.error(“Calculation exceeded maximum iterations.”);
break;
}
}

var totalInterestSaved = totalInterestWithoutPrepayment – totalInterestPaid;
var newLoanTermYears = Math.floor(months / 12);
var newLoanTermMonths = months % 12;

// Display results
document.getElementById(‘totalInterestSaved’).textContent = “Total Interest Saved: ” + formatCurrency(totalInterestSaved);
document.getElementById(‘newLoanTerm’).textContent = “New Loan Term: ” + newLoanTermYears + ” years, ” + newLoanTermMonths + ” months”;
document.getElementById(‘totalInterestPaid’).textContent = “Total Interest Paid: ” + formatCurrency(totalInterestPaid);
document.getElementById(‘totalPaymentsMade’).textContent = “Total Payments Made: ” + months;

document.getElementById(‘results’).style.display = ‘block’;

// Populate amortization table
populateAmortizationTable(amortizationData, standardMonthlyPayment, extraMonthlyPayment, paymentFrequency);

// Update chart
updateAmortizationChart(amortizationData, standardMonthlyPayment, extraMonthlyPayment, paymentFrequency);
}

function populateAmortizationTable(data, standardPayment, extraPayment, frequency) {
var tableBody = document.getElementById(‘amortizationTableBody’);
tableBody.innerHTML = ”; // Clear previous rows

var rowsToDisplay = Math.min(data.length, 20); // Display first 20 rows for brevity

for (var i = 0; i rowsToDisplay) {
var tr = document.createElement(‘tr’);
var td = document.createElement(‘td’);
td.colSpan = 7;
td.textContent = “… showing first ” + rowsToDisplay + ” of ” + data.length + ” payments.”;
td.style.textAlign = ‘center’;
td.style.fontStyle = ‘italic’;
tr.appendChild(td);
tableBody.appendChild(tr);
}
}

function updateAmortizationChart(data, standardPayment, extraPayment, frequency) {
var ctx = document.getElementById(‘amortizationChart’).getContext(‘2d’);

// Destroy previous chart instance if it exists
if (chartInstance) {
chartInstance.destroy();
}

var labels = data.map(function(item, index) {
return index maxDataPoints) {
var step = Math.floor(data.length / maxDataPoints);
for (var i = 0; i < data.length; i += step) {
sampledPrincipal.push(data[i].principal);
sampledInterest.push(data[i].interest);
sampledLabels.push(data[i].paymentNum);
}
// Ensure the last point is included if not perfectly divisible
if ((data.length – 1) % step !== 0) {
sampledPrincipal.push(data[data.length – 1].principal);
sampledInterest.push(data[data.length – 1].interest);
sampledLabels.push(data[data.length – 1].paymentNum);
}
} else {
sampledPrincipal = principalPaid;
sampledInterest = interestPaid;
sampledLabels = labels;
}

chartInstance = new Chart(ctx, {
type: 'bar', // Changed to bar chart for better visualization of monthly breakdown
data: {
labels: sampledLabels,
datasets: [{
label: 'Principal Paid',
data: sampledPrincipal,
backgroundColor: 'rgba(0, 74, 153, 0.6)', // Primary color
borderColor: 'rgba(0, 74, 153, 1)',
borderWidth: 1,
type: 'line', // Use line for principal reduction trend
fill: false,
tension: 0.1
}, {
label: 'Interest Paid',
data: sampledInterest,
backgroundColor: 'rgba(255, 99, 132, 0.6)', // A contrasting color
borderColor: 'rgba(255, 99, 132, 1)',
borderWidth: 1,
type: 'line', // Use line for interest trend
fill: false,
tension: 0.1
}]
},
options: {
responsive: true,
maintainAspectRatio: false,
scales: {
y: {
beginAtZero: true,
title: {
display: true,
text: 'Amount ($)'
}
},
x: {
title: {
display: true,
text: 'Payment Number'
}
}
},
plugins: {
title: {
display: true,
text: 'Monthly Principal vs. Interest Breakdown'
},
tooltip: {
callbacks: {
label: function(context) {
var label = context.dataset.label || '';
if (label) {
label += ': ';
}
if (context.parsed.y !== null) {
label += formatCurrency(context.parsed.y);
}
return label;
}
}
}
}
}
});
}

function resetCalculator() {
document.getElementById('loanAmount').value = "300000";
document.getElementById('interestRate').value = "4.5";
document.getElementById('loanTerm').value = "30";
document.getElementById('extraPayment').value = "200";
document.getElementById('paymentFrequency').value = "12";

document.getElementById('results').style.display = 'none';
document.getElementById('amortizationTableBody').innerHTML = ''; // Clear table
if (chartInstance) {
chartInstance.destroy(); // Destroy chart
chartInstance = null;
}
// Clear errors
document.getElementById('loanAmountError').style.display = 'none';
document.getElementById('interestRateError').style.display = 'none';
document.getElementById('loanTermError').style.display = 'none';
document.getElementById('extraPaymentError').style.display = 'none';
}

function copyResults() {
var resultsDiv = document.getElementById('results');
if (resultsDiv.style.display === 'none') {
alert("Please calculate the results first.");
return;
}

var mainResult = document.getElementById('totalInterestSaved').textContent;
var newTerm = document.getElementById('newLoanTerm').textContent;
var totalInterest = document.getElementById('totalInterestPaid').textContent;
var totalPayments = document.getElementById('totalPaymentsMade').textContent;

var loanAmount = document.getElementById('loanAmount').value;
var interestRate = document.getElementById('interestRate').value;
var loanTerm = document.getElementById('loanTerm').value;
var extraPayment = document.getElementById('extraPayment').value;
var paymentFrequency = document.getElementById('paymentFrequency').options[document.getElementById('paymentFrequency').selectedIndex].text;

var assumptions = `Key Assumptions:\n` +
`Original Loan Amount: ${formatCurrency(parseFloat(loanAmount))}\n` +
`Annual Interest Rate: ${interestRate}%\n` +
`Original Loan Term: ${loanTerm} years\n` +
`Monthly Extra Payment: ${formatCurrency(parseFloat(extraPayment))}\n` +
`Payment Frequency: ${paymentFrequency}`;

var textToCopy = `— Mortgage Prepayment Results —\n\n` +
`${mainResult}\n` +
`${newTerm}\n` +
`${totalInterest}\n` +
`${totalPayments}\n\n` +
`${assumptions}`;

// Use navigator.clipboard for modern browsers
if (navigator.clipboard && navigator.clipboard.writeText) {
navigator.clipboard.writeText(textToCopy).then(function() {
alert('Results copied to clipboard!');
}).catch(function(err) {
console.error('Failed to copy text: ', err);
// Fallback for older browsers or if clipboard API fails
copyToClipboardFallback(textToCopy);
});
} else {
copyToClipboardFallback(textToCopy);
}
}

// Fallback method for copying text
function copyToClipboardFallback(text) {
var textArea = document.createElement("textarea");
textArea.value = text;
textArea.style.position = "fixed"; // Avoid scrolling to bottom of page in MS Edge.
textArea.style.left = "-9999px";
textArea.style.top = "-9999px";
document.body.appendChild(textArea);
textArea.focus();
textArea.select();
try {
var successful = document.execCommand('copy');
var msg = successful ? 'Results copied to clipboard!' : 'Failed to copy results.';
alert(msg);
} catch (err) {
console.error('Fallback: Oops, unable to copy', err);
alert('Failed to copy results. Please copy manually.');
}
document.body.removeChild(textArea);
}

function toggleFaq(element) {
var content = element.nextElementSibling;
if (content.style.display === "block") {
content.style.display = "none";
} else {
content.style.display = "block";
}
}

// Initial calculation on page load
document.addEventListener('DOMContentLoaded', function() {
calculateMortgagePrepayment(); // Perform initial calculation with default values
});

// Add Chart.js library dynamically if not already present
(function() {
var script = document.createElement('script');
script.src = 'https://cdn.jsdelivr.net/npm/chart.js@3.7.0/dist/chart.min.js'; // Use a specific version
script.onload = function() {
console.log('Chart.js loaded successfully.');
// Now that Chart.js is loaded, we can proceed with initial calculation if needed
// calculateMortgagePrepayment(); // Uncomment if you want calculation on load after chart lib
};
script.onerror = function() {
console.error('Failed to load Chart.js library.');
alert('Error loading charting library. Charts may not display correctly.');
};
document.head.appendChild(script);
})();