Home Mortgage Interest Deduction Calculator

: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);
}
header {
background-color: var(–primary-color);
color: white;
padding: 20px 0;
text-align: center;
margin-bottom: 20px;
border-radius: 8px 8px 0 0;
}
header h1 {
margin: 0;
font-size: 2.5em;
}
.loan-calc-container {
background-color: var(–card-background);
padding: 30px;
border-radius: 8px;
box-shadow: var(–shadow);
margin-bottom: 30px;
}
.loan-calc-container h2 {
text-align: center;
color: var(–primary-color);
margin-bottom: 25px;
}
.input-group {
margin-bottom: 20px;
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: 100%;
padding: 12px;
border: 1px solid var(–border-color);
border-radius: 4px;
box-sizing: border-box;
font-size: 1em;
}
.input-group input[type=”number”]:focus,
.input-group input[type=”text”]:focus,
.input-group select:focus {
border-color: var(–primary-color);
outline: none;
box-shadow: 0 0 0 2px rgba(0, 74, 153, 0.2);
}
.input-group .helper-text {
font-size: 0.85em;
color: #666;
margin-top: 5px;
}
.error-message {
color: red;
font-size: 0.8em;
margin-top: 5px;
display: none; /* Hidden by default */
}
.button-group {
display: flex;
justify-content: space-between;
margin-top: 25px;
flex-wrap: wrap;
gap: 10px;
}
.button-group button {
padding: 12px 20px;
border: none;
border-radius: 4px;
cursor: pointer;
font-size: 1em;
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: #ffc107;
color: #212529;
}
.btn-copy:hover {
background-color: #e0a800;
}
#results {
margin-top: 30px;
padding: 25px;
background-color: var(–primary-color);
color: white;
border-radius: 8px;
text-align: center;
box-shadow: var(–shadow);
}
#results h3 {
margin-top: 0;
color: white;
font-size: 1.8em;
}
.result-item {
margin-bottom: 15px;
}
.result-item span {
font-weight: bold;
font-size: 1.2em;
}
.primary-result {
font-size: 2.2em !important;
font-weight: bold;
margin: 15px 0;
padding: 10px;
background-color: var(–success-color);
border-radius: 4px;
display: inline-block;
}
.intermediate-results, .formula-explanation {
margin-top: 20px;
padding: 15px;
background-color: #e9ecef;
border-radius: 4px;
color: var(–text-color);
text-align: left;
}
.intermediate-results h4, .formula-explanation h4 {
margin-top: 0;
color: var(–primary-color);
}
.chart-container {
margin-top: 30px;
padding: 25px;
background-color: var(–card-background);
border-radius: 8px;
box-shadow: var(–shadow);
text-align: center;
}
.chart-container h3 {
color: var(–primary-color);
margin-bottom: 20px;
}
canvas {
max-width: 100%;
height: auto;
}
table {
width: 100%;
border-collapse: collapse;
margin-top: 20px;
}
th, td {
padding: 10px;
border: 1px solid var(–border-color);
text-align: left;
}
th {
background-color: var(–primary-color);
color: white;
}
tbody tr:nth-child(even) {
background-color: #f2f2f2;
}
section {
margin-bottom: 40px;
padding: 30px;
background-color: var(–card-background);
border-radius: 8px;
box-shadow: var(–shadow);
}
section h2 {
color: var(–primary-color);
margin-top: 0;
border-bottom: 2px solid var(–primary-color);
padding-bottom: 10px;
margin-bottom: 20px;
}
section h3 {
color: var(–primary-color);
margin-top: 25px;
margin-bottom: 15px;
}
a {
color: var(–primary-color);
text-decoration: none;
}
a:hover {
text-decoration: underline;
}
.faq-list {
list-style: none;
padding: 0;
}
.faq-list li {
margin-bottom: 15px;
border-bottom: 1px dashed var(–border-color);
padding-bottom: 10px;
}
.faq-list li:last-child {
border-bottom: none;
}
.faq-question {
font-weight: bold;
color: var(–primary-color);
cursor: pointer;
display: block;
margin-bottom: 5px;
}
.faq-answer {
display: none;
padding-left: 10px;
font-size: 0.95em;
}
.internal-links-list {
list-style: none;
padding: 0;
}
.internal-links-list li {
margin-bottom: 10px;
}
.internal-links-list li a {
font-weight: bold;
}
.internal-links-list li p {
font-size: 0.9em;
color: #555;
margin-top: 3px;
}
@media (max-width: 768px) {
.container {
margin: 10px;
padding: 15px;
}
header h1 {
font-size: 1.8em;
}
.loan-calc-container, section {
padding: 20px;
}
.button-group button {
flex: 1 1 100%;
min-width: unset;
}
}

Calculate Your Potential Tax Savings

Mortgage Interest Deduction Calculator

Mortgage Amortization Schedule (First Year)

Month	Starting Balance	Payment	Interest Paid	Principal Paid	Ending Balance

Details of your mortgage payments for the first year.

What is the Home Mortgage Interest Deduction?

{primary_keyword} is a valuable tax benefit that allows homeowners to deduct the interest they pay on their mortgage debt from their taxable income. This deduction can significantly reduce a homeowner’s overall tax liability, making homeownership more affordable. It applies to interest paid on loans used to buy, build, or substantially improve a qualified home, which includes your main home and one other residence.

Who Should Use It:

Homeowners who itemize their deductions are the primary beneficiaries. If the total of your itemized deductions (including mortgage interest, state and local taxes up to $10,000, charitable contributions, etc.) exceeds the standard deduction for your filing status, then itemizing is beneficial. The {primary_keyword} is particularly advantageous for those with larger mortgages or higher interest rates, especially in the early years of their loan term when the majority of payments go towards interest.

Common Misconceptions:

• Deducting the entire mortgage payment: Only the interest portion is deductible, not the principal repayment.
• Deducting interest on any loan: The loan must be secured by your qualified home and used for specific purposes (buying, building, improving). Interest on home equity loans used for non-home-related expenses is generally not deductible.
• Unlimited deduction: There are limits on the amount of mortgage debt for which interest can be deducted ($750,000 for married filing jointly, $375,000 for married filing separately, for loans taken out after December 15, 2017). For older loans, the limit is $1 million ($500,000 MFS). Interest on home equity debt is deductible up to $100,000 ($50,000 MFS) if used to buy, build, or improve the home.
• Automatic benefit: You must itemize deductions to claim the {primary_keyword}. If your standard deduction is higher, you won’t benefit from itemizing mortgage interest.

Home Mortgage Interest Deduction Formula and Mathematical Explanation

Understanding the {primary_keyword} involves several steps, from calculating your total annual interest paid to determining the deductible portion based on IRS guidelines.

Step-by-Step Derivation:

1. Calculate Monthly Mortgage Payment (Principal & Interest): This uses the standard loan amortization formula.
2. Calculate Annual Interest Paid: Determine the total interest paid over the year by summing the interest portion of each monthly payment.
3. Calculate Deductible Home Equity Interest: If you have a HEL or HELOC, determine the interest paid on the portion of the loan used to buy, build, or improve your home.
4. Calculate Points Deduction: Determine if points paid qualify for immediate deduction or must be amortized over the loan term.
5. Determine Total Deductible Interest: Sum the deductible interest from the primary mortgage, deductible HEL/HELOC interest, and any deductible points, ensuring it does not exceed IRS limits for total mortgage debt.
6. Calculate Tax Savings: Multiply the total deductible interest by your marginal tax rate.

Variable Explanations:

The core calculation relies on understanding your mortgage details and tax situation.

Variable	Meaning	Unit	Typical Range
P (Principal Loan Amount)	The original amount borrowed for the mortgage.	$	$100,000 – $1,000,000+
r (Monthly Interest Rate)	The annual interest rate divided by 12.	Decimal (e.g., 0.045 / 12)	0.002 – 0.01
n (Number of Payments)	The total number of monthly payments over the loan term (Loan Term in Years * 12).	Months	180 – 360
Annual Interest Paid	Total interest paid on the mortgage over a 12-month period.	$	$5,000 – $30,000+ (especially early in loan)
Deductible HEL/HELOC Interest	Interest paid on home equity debt used for home improvements.	$	$0 – $10,000+
Points Paid	Fees paid directly to the lender at closing in exchange for a reduced interest rate.	$	0 – 3% of loan amount
Marginal Tax Rate	The tax rate applied to your last dollar of taxable income.	%	10% – 37% (Federal)
Taxable Income	Income after all adjustments and deductions.	$	$20,000 – $200,000+

Mathematical Explanation:

The monthly payment (M) is calculated using the formula: M = P [ r(1 + r)^n ] / [ (1 + r)^n – 1]. Each month, a portion of this payment covers interest, and the rest reduces the principal. The interest portion for a given month is calculated as: Interest = Outstanding Balance * r. The principal portion is: Principal = M – Interest. By summing the ‘Interest’ for 12 months, we get the Annual Interest Paid. The deductible amount is then capped by IRS limits on acquisition and home equity debt. Finally, Tax Savings = Total Deductible Interest * (Marginal Tax Rate / 100).

Practical Examples (Real-World Use Cases)

Let’s illustrate the {primary_keyword} with practical scenarios:

Example 1: First-Time Homebuyer

Scenario: Sarah buys her first home with a $300,000 mortgage at 5% interest for 30 years. Her taxable income is $70,000, and she falls into the 22% federal tax bracket. She paid 1 point ($3,000) at closing.

Inputs:

• Loan Amount: $300,000
• Interest Rate: 5%
• Loan Term: 30 years
• Taxable Income: $70,000
• Marginal Tax Rate: 22%
• Points Paid: $3,000
• HEL/HELOC: $0

Calculation Breakdown:

• Estimated Annual Interest Paid (Year 1): ~$14,700
• Deductible Interest (Primary Mortgage): ~$14,700 (assuming loan is within limits)
• Deductible Points: $3,000 (can often be deducted in the year paid)
• Total Potential Deductible Interest: ~$17,700
• Estimated Tax Savings: $17,700 * 0.22 = $3,894

Interpretation: Sarah can potentially reduce her taxable income by approximately $17,700, leading to an estimated tax saving of $3,894. This highlights the significant financial benefit of the {primary_keyword} for new homeowners.

Example 2: Refinancing and Home Improvement

Scenario: Mark refinanced his original mortgage and took out an additional $50,000 HELOC at 6% interest to renovate his kitchen. His original mortgage balance is $400,000 with a new rate of 4.5% for 25 years. His taxable income is $120,000, placing him in the 24% tax bracket. The HELOC interest for the year is $3,000.

Inputs:

• Loan Amount (Primary): $400,000
• Interest Rate (Primary): 4.5%
• Loan Term (Primary): 25 years
• Home Equity Loan Amount: $50,000
• HEL/HELOC Interest Rate: 6%
• Taxable Income: $120,000
• Marginal Tax Rate: 24%
• Points Paid: $0

Calculation Breakdown:

• Estimated Annual Interest Paid (Primary Mortgage, Year 1): ~$17,700
• Deductible HEL/HELOC Interest: $3,000 (since used for home improvement)
• Total Potential Deductible Interest: ~$17,700 + $3,000 = $20,700
• Estimated Tax Savings: $20,700 * 0.24 = $4,968

Interpretation: Mark’s ability to deduct both his primary mortgage interest and the interest from his HELOC (used for improvements) significantly increases his potential tax savings. He could save approximately $4,968 on his taxes, demonstrating how strategic use of home equity can enhance the benefits of the {primary_keyword}. Remember to check mortgage interest deduction limits.

How to Use This Home Mortgage Interest Deduction Calculator

Our calculator is designed for simplicity and accuracy. Follow these steps to estimate your potential {primary_keyword}:

1. Enter Primary Mortgage Details: Input your total mortgage loan amount, annual interest rate, and the loan term in years.
2. Enter Tax Information: Provide your total taxable income and your marginal federal tax rate (as a percentage).
3. Enter Home Equity Details (If Applicable): If you have a home equity loan or HELOC, enter the outstanding balance and its annual interest rate. Crucially, ensure this debt was used to buy, build, or substantially improve your home for the interest to be potentially deductible.
4. Enter Points Paid (Optional): If you paid points when obtaining your mortgage, enter the amount. Consult a tax advisor regarding specific deductibility rules.
5. Click ‘Calculate Deduction’: The calculator will instantly process your inputs.

How to Read Results:

• Estimated Annual Mortgage Interest Paid: Shows the total interest you’re projected to pay on your primary mortgage over 12 months.
• Estimated Deductible Interest: This is the portion of mortgage interest (including qualifying HELOC interest and points) that you may be able to deduct, subject to IRS limits.
• Estimated Tax Savings: Your potential reduction in federal income tax based on the deductible interest and your tax bracket.
• Primary Highlighted Result: This large, prominent number represents your estimated total tax savings.
• Key Figures: Provides a breakdown of the components contributing to your deductible interest.
• Chart & Table: Visualize your loan’s amortization and understand how payments are split between interest and principal.

Decision-Making Guidance:

Use the results to determine if itemizing deductions is beneficial for you. If your calculated deductible mortgage interest, combined with other potential itemized deductions (like state and local taxes up to $10,000, charitable donations), exceeds your standard deduction amount, itemizing is likely advantageous. Always consult with a qualified tax professional for personalized advice, as tax laws can be complex and your specific situation may have unique factors.

Key Factors That Affect Home Mortgage Interest Deduction Results

Several elements influence the amount of mortgage interest you can deduct and the resulting tax savings. Understanding these factors is crucial for accurate estimation and financial planning:

1. Mortgage Principal Balance: A higher loan amount generally means more interest paid, especially early in the loan term. However, the IRS limits the principal amount on which interest is deductible ($750,000/$375,000 for newer loans, $1M/$500K for older ones).
2. Interest Rate: A higher interest rate directly increases the amount of interest paid each month and annually. This significantly boosts the potential deduction, particularly in the initial years of the mortgage. Explore current mortgage rates for context.
3. Loan Term: Shorter loan terms (e.g., 15 years) result in higher monthly payments but pay down principal faster and accrue less total interest over the life of the loan compared to longer terms (e.g., 30 years). However, in the early years, a 30-year loan often generates more deductible interest than a 15-year loan with the same rate and principal.
4. Home Equity Debt Usage: Interest on home equity loans (HELs) and lines of credit (HELOCs) is only deductible if the funds were used to buy, build, or substantially improve the qualified residence securing the loan. Interest on funds used for other purposes (e.g., paying off credit cards, education) is not deductible. There’s also a limit of $100,000 ($50,000 MFS) on deductible home equity debt.
5. Points Paid: Points are prepaid interest. While often deductible in the year paid, specific rules apply (e.g., must be customary, loan must be for primary residence, points cannot exceed 3% of loan amount unless it’s a purchase). Consult a tax advisor.
6. Taxable Income and Marginal Tax Rate: The actual tax savings depend on your income level and tax bracket. A higher tax rate means each dollar of deduction saves you more in taxes. For example, a $1,000 deduction saves $320 if you’re in the 32% bracket but only $220 if you’re in the 22% bracket.
7. Itemizing vs. Standard Deduction: The {primary_keyword} only benefits taxpayers who itemize their deductions. If your total itemized deductions are less than the standard deduction amount for your filing status, you won’t get a tax benefit from mortgage interest.

Frequently Asked Questions (FAQ)

• Can I deduct mortgage interest if I didn’t itemize?
  No, the home mortgage interest deduction is an itemized deduction. You can only claim it if your total itemized deductions exceed the standard deduction amount for your filing status.
• What are the limits on deductible mortgage interest?
  For loans taken out after December 15, 2017, you can deduct interest on up to $750,000 of mortgage debt ($375,000 if married filing separately). For loans before that date, the limit is $1 million ($500,000 MFS). Interest on home equity debt is deductible up to $100,000 ($50,000 MFS) if used to buy, build, or improve your home.
• Is interest on a home equity loan always deductible?
  No. Interest on a home equity loan or HELOC is only deductible if the loan proceeds were used to buy, build, or substantially improve the qualified residence that secures the loan.
• Can I deduct interest paid on a second home?
  Yes, you can generally deduct mortgage interest paid on a second home if it qualifies as a second residence and the loan meets the requirements for acquisition or home equity indebtedness, subject to the same debt limits.
• What if I paid points on my mortgage?
  Points paid to obtain a mortgage on your primary residence are generally deductible in the year paid, provided certain conditions are met. Points paid on refinancing may need to be amortized over the life of the loan. Consult a tax professional.
• How does refinancing affect my deduction?
  If you refinance your original mortgage, the new loan generally inherits the acquisition debt limits and start date of the original loan, potentially allowing you to deduct interest on a larger amount. However, if the refinance cash-out exceeds the original loan amount or is used for purposes other than home improvement, the excess may be treated as home equity debt.
• Does the calculator account for state and local tax (SALT) deductions?
  This calculator focuses specifically on mortgage interest. While SALT deductions are often itemized alongside mortgage interest, they are subject to a $10,000 annual limit per household. You need to consider all your potential itemized deductions to see if they exceed the standard deduction.
• What is the difference between acquisition debt and home equity debt for deduction purposes?
  Acquisition debt is money used to buy, build, or substantially improve your main home or second home. Home equity debt is a loan secured by your home, but the interest is only deductible if the funds are used for home improvements. There are different limits for each type of debt.

Related Tools and Internal Resources

• Mortgage Affordability Calculator

  Estimate how much house you can afford based on your income, debts, and desired monthly payment.

• Mortgage Refinance Calculator

  Determine if refinancing your current mortgage could save you money.

• Property Tax Calculator

  Estimate your annual property taxes based on home value and local rates.

• Home Equity Loan vs. HELOC Guide

  Understand the differences between home equity loans and lines of credit.

• Understanding Tax Brackets

  Learn how marginal tax rates work and how they affect your tax liability.

• Standard Deduction vs. Itemizing Guide

  Helpful information to decide whether to take the standard deduction or itemize your expenses.

var loanAmountInput = document.getElementById(‘loanAmount’);
var interestRateInput = document.getElementById(‘interestRate’);
var loanTermInput = document.getElementById(‘loanTerm’);
var taxableIncomeInput = document.getElementById(‘taxableIncome’);
var taxBracketInput = document.getElementById(‘taxBracket’);
var homeEquityLoanAmountInput = document.getElementById(‘homeEquityLoanAmount’);
var homeEquityLoanInterestRateInput = document.getElementById(‘homeEquityLoanInterestRate’);
var pointsPaidInput = document.getElementById(‘pointsPaid’);

var loanAmountError = document.getElementById(‘loanAmountError’);
var interestRateError = document.getElementById(‘interestRateError’);
var loanTermError = document.getElementById(‘loanTermError’);
var taxableIncomeError = document.getElementById(‘taxableIncomeError’);
var taxBracketError = document.getElementById(‘taxBracketError’);
var homeEquityLoanAmountError = document.getElementById(‘homeEquityLoanAmountError’);
var homeEquityLoanInterestRateError = document.getElementById(‘homeEquityLoanInterestRateError’);
var pointsPaidError = document.getElementById(‘pointsPaidError’);

var annualInterestPaidSpan = document.getElementById(‘annualInterestPaid’);
var deductibleInterestSpan = document.getElementById(‘deductibleInterest’);
var taxSavingsSpan = document.getElementById(‘taxSavings’);
var primaryResultSpan = document.getElementById(‘primaryResult’);

var totalAnnualInterestSpan = document.getElementById(‘totalAnnualInterest’);
var deductibleHelocInterestSpan = document.getElementById(‘deductibleHelocInterest’);
var totalDeductibleInterestSpan = document.getElementById(‘totalDeductibleInterest’);
var pointsDeductionSpan = document.getElementById(‘pointsDeduction’);

var amortizationTableBody = document.getElementById(‘amortizationTable’).getElementsByTagName(‘tbody’)[0];
var mortgageChartCanvas = document.getElementById(‘mortgageChart’);
var mortgageChart;

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

function formatPercent(amount) {
return amount.toFixed(2) + “%”;
}

function validateInput(input, errorElement, min, max) {
var value = parseFloat(input.value);
var isValid = true;
if (isNaN(value)) {
errorElement.textContent = “Please enter a valid number.”;
errorElement.style.display = ‘block’;
isValid = false;
} else if (value max) {
errorElement.textContent = “Value cannot exceed ” + max + “.”;
errorElement.style.display = ‘block’;
isValid = false;
} else {
errorElement.textContent = “”;
errorElement.style.display = ‘none’;
}
return isValid;
}

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

function calculateDeduction() {
var loanAmount = parseFloat(loanAmountInput.value);
var interestRate = parseFloat(interestRateInput.value);
var loanTerm = parseInt(loanTermInput.value);
var taxableIncome = parseFloat(taxableIncomeInput.value);
var taxBracket = parseFloat(taxBracketInput.value);
var homeEquityLoanAmount = parseFloat(homeEquityLoanAmountInput.value);
var homeEquityLoanInterestRate = parseFloat(homeEquityLoanInterestRateInput.value);
var pointsPaid = parseFloat(pointsPaidInput.value);

var isValid = true;
isValid &= validateInput(loanAmountInput, loanAmountError, 0);
isValid &= validateInput(interestRateInput, interestRateError, 0);
isValid &= validateInput(loanTermInput, loanTermError, 1);
isValid &= validateInput(taxableIncomeInput, taxableIncomeError, 0);
isValid &= validateInput(taxBracketInput, taxBracketError, 0, 100);
isValid &= validateInput(homeEquityLoanAmountInput, homeEquityLoanAmountError, 0);
isValid &= validateInput(homeEquityLoanInterestRateInput, homeEquityLoanInterestRateError, 0);
isValid &= validateInput(pointsPaidInput, pointsPaidError, 0);

if (!isValid) {
resetResults();
return;
}

var monthlyPayment = calculateMonthlyPayment(loanAmount, interestRate, loanTerm);
var monthlyRate = interestRate / 100 / 12;
var numPayments = loanTerm * 12;

var totalInterestPaidYear1 = 0;
var principalPaidYear1 = 0;
var currentBalance = loanAmount;
var amortizationData = [];

for (var i = 0; i < numPayments; i++) {
var interestPayment = currentBalance * monthlyRate;
var principalPayment = monthlyPayment – interestPayment;

if (principalPayment < 0) principalPayment = 0; // Handle potential floating point issues
if (interestPayment < 0) interestPayment = 0;

currentBalance -= principalPayment;
if (currentBalance < 0) currentBalance = 0; // Ensure balance doesn't go negative

if (i < 12) {
totalInterestPaidYear1 += interestPayment;
principalPaidYear1 += principalPayment;
amortizationData.push({
month: i + 1,
startBalance: loanAmount – (principalPaidYear1 – principalPayment),
payment: monthlyPayment,
interest: interestPayment,
principal: principalPayment,
endBalance: currentBalance
});
} else {
break; // Only need first year for table and annual interest
}
}

// Ensure total interest calculation is robust
var calculatedTotalInterest = 0;
var tempBalance = loanAmount;
for(var i = 0; i < numPayments; i++) {
var interestForMonth = tempBalance * monthlyRate;
calculatedTotalInterest += interestForMonth;
var principalForMonth = monthlyPayment – interestForMonth;
tempBalance -= principalForMonth;
if (tempBalance 0 && homeEquityLoanInterestRate > 0) {
// Assuming HELOC interest is fully deductible if used for home improvement, up to limits
// For simplicity, we calculate annual interest on HELOC based on the amount provided.
// Real-world scenarios might involve fluctuating balances.
deductibleHelocInterest = homeEquityLoanAmount * (homeEquityLoanInterestRate / 100);
}

var pointsDeduction = pointsPaid; // Simplified: assume points are deductible in full if paid. Real rules are complex.

// IRS Limits (Simplified for calculation)
var acquisitionDebtLimit = 750000; // For loans after Dec 15, 2017
var homeEquityDebtLimit = 100000; // For funds used to buy/build/improve home

var totalMortgageDebt = loanAmount + homeEquityLoanAmount;
var deductibleInterest = 0;
var remainingAcquisitionLimit = acquisitionDebtLimit – loanAmount; // If loanAmount > limit, this is negative
var remainingEquityLimit = homeEquityDebtLimit – homeEquityLoanAmount; // If HELOC > limit, this is negative

var deductiblePrimaryInterest = Math.max(0, totalInterestPaidYear1);
var deductiblePoints = Math.max(0, pointsDeduction);

// Determine deductible amounts based on limits
var finalDeductibleInterest = 0;
var finalDeductibleHeloc = 0;
var finalDeductiblePoints = 0;

// Deduct primary mortgage interest first, up to the acquisition debt limit
if (loanAmount <= acquisitionDebtLimit) {
finalDeductibleInterest = deductiblePrimaryInterest;
} else {
// If loan exceeds limit, need to prorate interest or use specific IRS methods.
// Simplified: Assume interest is proportional to the deductible portion of the loan.
finalDeductibleInterest = deductiblePrimaryInterest * (acquisitionDebtLimit / loanAmount);
}

// Deduct HELOC interest, up to the home equity debt limit
if (homeEquityLoanAmount acquisitionDebtLimit + homeEquityDebtLimit) {
// If total debt exceeds combined limits, need to prorate.
// This is highly simplified.
effectiveTotalDeductible = totalDeductible * ((acquisitionDebtLimit + homeEquityDebtLimit) / totalMortgageDebt);
}

deductibleInterest = Math.min(totalDeductible, effectiveTotalDeductible); // Final capped value
deductibleInterest = Math.max(0, deductibleInterest); // Ensure non-negative

var estimatedTaxSavings = deductibleInterest * (taxBracket / 100);

primaryResultSpan.textContent = formatCurrency(estimatedTaxSavings);
taxSavingsSpan.textContent = formatCurrency(estimatedTaxSavings);
deductibleInterestSpan.textContent = formatCurrency(deductibleInterest);
annualInterestPaidSpan.textContent = formatCurrency(totalInterestPaidYear1);

totalAnnualInterestSpan.textContent = formatCurrency(totalInterestPaidYear1);
deductibleHelocInterestSpan.textContent = formatCurrency(finalDeductibleHeloc);
totalDeductibleInterestSpan.textContent = formatCurrency(deductibleInterest);
pointsDeductionSpan.textContent = formatCurrency(finalDeductiblePoints);

updateChart(amortizationData, monthlyPayment);
updateAmortizationTable(amortizationData);
}

function resetResults() {
annualInterestPaidSpan.textContent = “$0.00”;
deductibleInterestSpan.textContent = “$0.00”;
taxSavingsSpan.textContent = “$0.00”;
primaryResultSpan.textContent = “$0.00”;

totalAnnualInterestSpan.textContent = “–“;
deductibleHelocInterestSpan.textContent = “–“;
totalDeductibleInterestSpan.textContent = “–“;
pointsDeductionSpan.textContent = “–“;

if (mortgageChart) {
mortgageChart.destroy();
}
amortizationTableBody.innerHTML = ”;
}

function resetCalculator() {
loanAmountInput.value = “300000”;
interestRateInput.value = “4.5”;
loanTermInput.value = “30”;
taxableIncomeInput.value = “80000”;
taxBracketInput.value = “22”;
homeEquityLoanAmountInput.value = “0”;
homeEquityLoanInterestRateInput.value = “0”;
pointsPaidInput.value = “0”;

// Clear errors
loanAmountError.textContent = “”; loanAmountError.style.display = ‘none’;
interestRateError.textContent = “”; interestRateError.style.display = ‘none’;
loanTermError.textContent = “”; loanTermError.style.display = ‘none’;
taxableIncomeError.textContent = “”; taxableIncomeError.style.display = ‘none’;
taxBracketError.textContent = “”; taxBracketError.style.display = ‘none’;
homeEquityLoanAmountError.textContent = “”; homeEquityLoanAmountError.style.display = ‘none’;
homeEquityLoanInterestRateError.textContent = “”; homeEquityLoanInterestRateError.style.display = ‘none’;
pointsPaidError.textContent = “”; pointsPaidError.style.display = ‘none’;

resetResults();
}

function copyResults() {
var resultsText = “— Mortgage Interest Deduction Estimate —\n\n”;
resultsText += “Primary Result (Estimated Tax Savings): ” + primaryResultSpan.textContent + “\n”;
resultsText += “Estimated Annual Mortgage Interest Paid: ” + annualInterestPaidSpan.textContent + “\n”;
resultsText += “Estimated Deductible Interest: ” + deductibleInterestSpan.textContent + “\n”;
resultsText += “Estimated Tax Savings: ” + taxSavingsSpan.textContent + “\n\n”;

resultsText += “Key Figures:\n”;
resultsText += “- Total Annual Interest Paid (Primary Mortgage): ” + totalAnnualInterestSpan.textContent + “\n”;
resultsText += “- Deductible Interest from HEL/HELOC: ” + deductibleHelocInterestSpan.textContent + “\n”;
resultsText += “- Total Potential Deductible Interest: ” + totalDeductibleInterestSpan.textContent + “\n”;
resultsText += “- Points Deduction (if applicable): ” + pointsDeductionSpan.textContent + “\n\n”;

resultsText += “Assumptions:\n”;
resultsText += “- Loan Amount: ” + formatCurrency(parseFloat(loanAmountInput.value)) + “\n”;
resultsText += “- Interest Rate: ” + formatPercent(parseFloat(interestRateInput.value)) + “\n”;
resultsText += “- Loan Term: ” + loanTermInput.value + ” years\n”;
resultsText += “- Taxable Income: ” + formatCurrency(parseFloat(taxableIncomeInput.value)) + “\n”;
resultsText += “- Marginal Tax Rate: ” + formatPercent(parseFloat(taxBracketInput.value)) + “\n”;
resultsText += “- HEL/HELOC Amount: ” + formatCurrency(parseFloat(homeEquityLoanAmountInput.value)) + “\n”;
resultsText += “- HEL/HELOC Interest Rate: ” + formatPercent(parseFloat(homeEquityLoanInterestRateInput.value)) + “\n”;
resultsText += “- Points Paid: ” + formatCurrency(parseFloat(pointsPaidInput.value)) + “\n”;
resultsText += “\nDisclaimer: This is an estimate. Consult a tax professional.”;

navigator.clipboard.writeText(resultsText).then(function() {
alert(‘Results copied to clipboard!’);
}, function(err) {
console.error(‘Could not copy text: ‘, err);
alert(‘Failed to copy results. Please copy manually.’);
});
}

function updateAmortizationTable(data) {
amortizationTableBody.innerHTML = ”; // Clear previous rows
data.forEach(function(row) {
var tr = amortizationTableBody.insertRow();
tr.insertCell().textContent = row.month;
tr.insertCell().textContent = formatCurrency(row.startBalance);
tr.insertCell().textContent = formatCurrency(row.payment);
tr.insertCell().textContent = formatCurrency(row.interest);
tr.insertCell().textContent = formatCurrency(row.principal);
tr.insertCell().textContent = formatCurrency(row.endBalance);
});
}

function updateChart(amortizationData, monthlyPayment) {
if (mortgageChart) {
mortgageChart.destroy();
}

var ctx = mortgageChartCanvas.getContext(‘2d’);
var labels = amortizationData.map(function(item) { return ‘Month ‘ + item.month; });
var interestData = amortizationData.map(function(item) { return item.interest; });
var principalData = amortizationData.map(function(item) { return item.principal; });

mortgageChart = new Chart(ctx, {
type: ‘bar’,
data: {
labels: labels,
datasets: [{
label: ‘Interest Paid’,
data: interestData,
backgroundColor: ‘rgba(0, 74, 153, 0.6)’,
borderColor: ‘rgba(0, 74, 153, 1)’,
borderWidth: 1
}, {
label: ‘Principal Paid’,
data: principalData,
backgroundColor: ‘rgba(40, 167, 69, 0.6)’,
borderColor: ‘rgba(40, 167, 69, 1)’,
borderWidth: 1
}]
},
options: {
responsive: true,
maintainAspectRatio: false,
scales: {
y: {
beginAtZero: true,
title: {
display: true,
text: ‘Amount ($)’
}
},
x: {
title: {
display: true,
text: ‘Payment Period’
}
}
},
plugins: {
tooltip: {
callbacks: {
footer: function(tooltipItems) {
var total = 0;
tooltipItems.forEach(function(tooltipItem) {
total += tooltipItem.raw;
});
return ‘Total Payment: ‘ + formatCurrency(total);
}
}
}
}
}
});
}

// Initial calculation on load
document.addEventListener(‘DOMContentLoaded’, function() {
calculateDeduction();

// Add event listeners for real-time updates
var inputs = document.querySelectorAll(‘.loan-calc-container input[type=”number”], .loan-calc-container select’);
inputs.forEach(function(input) {
input.addEventListener(‘input’, calculateDeduction);
});

// FAQ functionality
var faqQuestions = document.querySelectorAll(‘.faq-question’);
faqQuestions.forEach(function(question) {
question.addEventListener(‘click’, function() {
var answer = this.nextElementSibling;
if (answer.style.display === ‘block’) {
answer.style.display = ‘none’;
} else {
answer.style.display = ‘block’;
}
});
});
});