Is Portfolio Line of Credit Interest Tax Deductible?

Interest on a portfolio line of credit is tax deductible only when you can trace the borrowed money to a qualifying use, such as a taxable investment, a trade or business, or a passive activity. The IRS doesn’t care that your brokerage account secures the loan. It cares where each dollar you drew actually went. Spend it on taxable investments and the interest lands in a deductible category, subject to annual limits. Spend it on a kitchen remodel or a car, and the interest is personal, which means no deduction at all.

The Use of the Money Decides It

Internal Revenue Code Section 163 ties the tax treatment of interest to the use of the loan proceeds, not to the collateral behind the loan.¹ Temporary Treasury Regulation 1.163-8T lays out exactly how taxpayers must trace borrowed dollars from the moment they leave the credit line to the moment they’re spent.² The interest then goes into one of four buckets: investment, business, passive activity, or personal. Each bucket has its own deduction rules, and each dollar is allocated on a daily basis for the time it stays in that category.

One quirk of a PLOC that shapes the tax question from the start: the loan agreement, backed by federal securities regulations, generally forbids using proceeds to buy more securities or pay off a margin loan. So the common tax strategy of “borrowing to buy stock” doesn’t apply here. The deductible uses that remain are investments other than securities, business expenditures, and passive activity funding.

When the Interest Is Deductible

Investment Interest

PLOC proceeds used to purchase or carry property held for investment produce interest classified as investment interest under IRC Section 163(d).¹ This is the deductible bucket most PLOC borrowers aim for, but it comes with a hard ceiling: the deduction is capped at your net investment income (NII) for the year.

NII equals your investment income minus your investment expenses. Investment income includes taxable interest, non-qualified dividends, royalties, annuities, and short-term capital gains from investment property.³ It does not include passive activity income, which has its own rules. On the expense side, miscellaneous itemized deductions subject to the 2-percent floor were suspended by the Tax Cuts and Jobs Act and made permanently gone starting in 2026 by the One Big Beautiful Bill Act. For most individuals, investment expenses now effectively equal zero, so NII equals investment income.

Long-term capital gains and qualified dividends sit outside NII by default, which preserves their preferential tax rates. You can elect on Form 4952 to include some or all of them in NII to raise the deduction cap, but every dollar you move in loses the preferential rate and gets taxed as ordinary income.³ Run the numbers both ways before you file.

Investment interest you can’t use this year isn’t lost. It carries forward indefinitely and offsets NII in future years.⁴

One other hurdle: investment interest is an itemized deduction on Schedule A.⁵ You get no benefit if you take the standard deduction. For 2026, that’s $16,100 for single filers and $32,200 for married couples filing jointly.⁶ If your total itemized deductions don’t clear that bar, the investment interest write-off is just paperwork.

Business Interest

PLOC funds poured into a trade or business produce business interest, which is generally deductible but subject to the Section 163(j) cap. The limit is the sum of your business interest income plus 30 percent of your adjusted taxable income from the business.¹ Any disallowed amount carries forward indefinitely.

Small businesses are exempt from the 163(j) cap entirely. The threshold is average annual gross receipts of $31 million or less over the prior three years (the most recent inflation-adjusted figure).⁷

Passive Activity Interest

If you use the proceeds to fund a passive activity, such as buying into rental real estate where you don’t materially participate, the interest becomes passive activity interest. Under IRC Section 469, it’s deductible only against net income from your passive activities.⁸ Any excess is suspended and carried forward until you generate enough passive income to absorb it, or until you sell the entire activity in a fully taxable transaction.

When It Isn’t Deductible

Personal Spending

PLOC funds used for personal expenses, whether paying off credit cards, financing a vacation, or buying a car, produce personal interest. IRC Section 163(h) makes personal interest completely non-deductible.¹ There’s no carryforward, no exception for high earners, no workaround. This is also the default classification the IRS applies when your records can’t support something better.

Tax-Exempt Investments

Using PLOC proceeds to buy or carry tax-exempt obligations like municipal bonds knocks out the interest deduction entirely. IRC Section 265 bars deducting interest on debt incurred to carry investments whose income is exempt from federal tax.⁹ This trips up taxpayers who hold both taxable and tax-exempt bonds in the same portfolio and borrow against the combined balance.

Keeping the Trace Clean

The simplest way to satisfy the tracing rules is to deposit PLOC draws into a dedicated account and spend them on one category of expenditure. Mix borrowed dollars with your regular checking balance and the regulation’s ordering rules take over: debt proceeds are treated as spent before any unborrowed funds already sitting there and before any later deposits.² That default can push your borrowed dollars toward expenditures you didn’t intend.

There is one useful shortcut. If you make an expenditure from the account within 15 days after depositing the draw, the regulation lets you treat that expenditure as made from the borrowed funds, even if the default ordering would say otherwise.² It’s 15 days, not 30; the 30-day reference in the regulation covers a separate interest-calculation rule.

If you use the same line for different purposes over time, each draw is traced separately and interest on the outstanding balance is split across categories on a daily basis. The regulation also sets the order in which payments reduce the different debt categories:¹⁰

Personal expenditures are paid down first.
Investment and general passive activity expenditures come next.
Active rental real estate follows.
Former passive activity debt is next.
Trade or business expenditures are paid down last.

That ordering works in your favor. Paying down the line reduces the non-deductible personal portion first, leaving the deductible categories outstanding longer. If you have limited cash to put toward the balance, the default naturally preserves the deductible interest.

Contemporaneous records are everything. Keep documentation showing the date and amount of each draw, the account it landed in, and the expenditure it funded, with receipts or transfer confirmations to back it up. Your brokerage reports total PLOC interest on your account statements, but there’s no 1098-style form that breaks it out by category. You are solely responsible for the split, and if the IRS questions your allocation and you can’t produce a clear paper trail, the default is reclassification as non-deductible personal interest.

What You File

The interest moves to different forms depending on how it’s classified:

Investment interest: calculated on Form 4952 and claimed on Schedule A as an itemized deduction. Taxpayers subject to the AMT may need an adjustment on Form 6251.⁴¹¹
Business interest: reported on Schedule C for sole proprietors, or on the appropriate partnership or corporate return, subject to the Section 163(j) cap.¹²
Passive activity interest: run through Form 8582 for the passive loss limitation, then reported on Schedule E.¹³¹⁴
Personal interest: not reported anywhere as a deduction, because it isn’t one.

What Happens If You Get It Wrong

Deducting PLOC interest that should have been personal interest can trigger the accuracy-related penalty under IRC Section 6662: 20 percent of the underpayment attributable to negligence or a substantial understatement of tax.¹⁵ A substantial understatement exists when the shortfall exceeds the greater of 10 percent of the tax due or $5,000. Where the IRS can show intentional evasion, the civil fraud penalty under Section 6663 climbs to 75 percent of the underpayment.¹⁶ The 20-percent negligence penalty is the realistic danger for most borrowers, and it’s the one that falls on taxpayers who simply didn’t keep adequate records.

1
Office of the Law Revision Counsel. 26 USC 163 – Interest
2
govinfo.gov. 26 CFR 1.163-8T Allocation of Interest Expense Among Expenditures (Temporary)
3
Internal Revenue Service. Publication 550 – Investment Income and Expenses
4
Internal Revenue Service. About Form 4952 – Investment Interest Expense Deduction
5
Internal Revenue Service. Topic No. 505 – Interest Expense
6
Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
7
Internal Revenue Service. Questions and Answers About the Limitation on the Deduction for Business Interest Expense
8
Office of the Law Revision Counsel. 26 USC 469 – Passive Activity Losses and Credits Limited
9
Office of the Law Revision Counsel. 26 USC 265 – Expenses and Interest Relating to Tax-Exempt Income
10
eCFR. 26 CFR 1.163-8T – Allocation of Interest Expense Among Expenditures (Temporary)
11
Internal Revenue Service. About Schedule A (Form 1040) – Itemized Deductions
12
Internal Revenue Service. 2025 Instructions for Schedule C (Form 1040)
13
Internal Revenue Service. Instructions for Form 8582 – Passive Activity Loss Limitations
14
Internal Revenue Service. About Schedule E (Form 1040) – Supplemental Income and Loss
15
Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments
16
Internal Revenue Service. Return Related Penalties