Most retirement savers learn one rule about IRAs and taxes: nothing is taxed until you take it out. That rule has an exception written directly into the Internal Revenue Code, and it is about to matter to more people. The Labor Department's March 2026 proposed safe harbor for alternative assets in 401(k) menus drew nearly 37,000 public comments, and partnership-structured investments are already common inside self-directed IRAs.
When a retirement account holds the wrong kind of income, the account itself becomes a taxpayer.
What Triggers It
Under IRC §512, an otherwise tax-exempt entity — including an IRA, Roth IRA, SEP, SIMPLE, HSA, or Coverdell — owes tax on unrelated business taxable income (UBTI): income from a trade or business regularly carried on that isn't related to its exempt purpose. Two common triggers:
Operating income from partnerships. Master limited partnerships and private LPs pass their share of business income through to you on a Schedule K-1. The UBTI amount appears in Box 20V. Baird's Wealth Solutions Group notes this figure "is often a relatively small amount," and a single modest MLP position typically doesn't trip the threshold — but that is a fact about size, not a safe harbor.
Debt-financed income. IRC §514 strips the usual exemption from income produced by property carrying "acquisition indebtedness." A leveraged real estate deal inside a self-directed IRA is the classic case: the taxable percentage is average acquisition debt divided by average adjusted basis.
How the Tax Is Calculated and Paid
Section 512(b)(12) allows a $1,000 specific deduction. Once UBTI reaches $1,000, the custodian must file Form 990-T — by the 15th day of the fourth month after year-end, so April 15 for calendar-year accounts.
The rate schedule is the one for trusts, and it is brutally compressed. Under Revenue Procedure 2025-32, a trust reaches the top 37% rate at just $16,000 of taxable income in 2026. A single individual doesn't get there until $640,600.
Critically, the tax is paid from inside the account. Fidelity's fact sheet is explicit that the payment is wired to the IRS from account assets and is not reported on a Form 1099-R. Custodians are consistent that the liability must be satisfied with IRA funds rather than the owner's personal money, so the tax permanently reduces your retirement balance. And an extension on Form 8868 extends the filing date, not the payment date: late-payment penalties run 0.5% per month up to 25%, with daily interest.
The Trap Most Investors Miss
Years of trivial Box 20V numbers can end in one large bill. When an MLP is sold, the depreciation deductions that made your distributions tax-deferred are recaptured as ordinary income — and that recapture is UBTI, even though no money left the IRA. The longer you held it, the larger it is.
Three Practical Steps
- Send your custodian the cost basis. Fidelity's fact sheet states that if you don't provide basis on an LP sale and no K-1 arrives, it uses $0.00 — taxing the entire proceeds.
- Send the debt ratio, too. Absent partnership data, Fidelity "takes the most conservative position and assumes that the debt-ratio is 100%."
- Supply loss carryovers. Custodians assume no prior-year net operating losses unless you provide the schedule. Accumulated MLP losses become deductible in the year of sale.
If you want partnership exposure without this machinery, MLP funds structured as C-corporations block the pass-through — at the cost of an entity-level tax. As with the 28% collectibles rate on metals, the wrapper decides the tax, not the asset.
Sources: IRS Instructions for Form 990-T; 26 U.S.C. §512 and §514 (Cornell LII); Fidelity Form 990-T Fact Sheet and UBTI tax topic; Robert W. Baird & Co. Wealth Solutions Group, The Taxation of Master Limited Partnerships FAQ (September 2025); Revenue Procedure 2025-32 via Greenleaf Trust; U.S. Department of Labor proposed rule on designated investment alternatives (March 2026).