Operating Rules: How to Trace Cleanly
Treas. Reg. §1.163-8T prescribes the rules that determine which expenditures the IRS will treat as funded by which loan dollars. Two of them govern how an active borrower should operate day to day.
Use a dedicated conduit account. The single largest source of audit friction is commingling. If a $500,000 SBLOC draw lands in your everyday checking account already holding $80,000 of salary income, and you then spend $300,000 on equities and $70,000 on a car from that account, the IRS applies the allocation rules of Treas. Reg. §1.163-8T(c)(4) to decide which dollars went where — and the answer is not the one you wanted. Open a separate checking account whose only inflows are loan proceeds and whose only outflows are traceable expenditures of one category. Five minutes a year of bookkeeping saves the deduction.
The 30-day window. Two timing rules stack here, and citing the right one matters on examination. The regulation itself ( Treas. Reg. §1.163-8T(c)(4)(iii)(B)) lets you treat an expenditure made within 15 days of depositing loan proceeds into an account as funded from those proceeds, regardless of what else sits in the account. IRS Notice 89-35 (1989-1 C.B. 675) then widens it: you may elect to treat any expenditure made within 30 days before or after the proceeds are received as funded by them. This gives a buffer for fast reallocation without breaking the trace. It does not mean every expenditure in a 60-day window automatically traces to the loan — only that you may elect that treatment when the timing supports it. Move within the window, or document why you could not.
The muni-bond trap. IRC §265 disallows the interest deduction on any debt incurred or continued to purchase or carry tax-exempt obligations. If you draw an SBLOC, trace the proceeds into a taxable portfolio, and elsewhere in your accounts hold substantial municipal bond positions, the IRS can argue that you are effectively using the loan to “continue” the muni position — the theory being that you could have sold munis to fund the equity purchase instead of borrowing. The case law is fact-specific and unfriendly to the taxpayer. Safe play: if you are running the debt swap below, do not hold material munis in the post-swap portfolio, and do not buy any with traced loan proceeds.
Tax-sheltered accounts disqualify. Borrowing to fund a Roth IRA, HSA, or 529 contribution disqualifies the interest entirely under IRC §265 — the IRS treats the contribution as buying tax-exempt income. The year-end “borrow on the HELOC to top up the Roth” move that sometimes appears in personal-finance blogs is precisely the trap the section was written for.