The IRA cash-on-cash comparison almost always ignores the line that changes it most

The UDFI point is the one most people get wrong in the direction you did not mention: the exposure runs on the leveraged fraction of the asset, so a preferred equity slice in a deal with a 65 percent LTV loan does not expose the full preferred balance to UBIT, only the portion proportionate to acquisition indebtedness. That matters when you are comparing structures because a lightly leveraged deal can carry preferred equity with very little UDFI drag while still giving you the deployment efficiency you described.

The cycle-rate framing is right, and the number worth adding to it is the custodian's annual account fee divided across the average deployed balance, which on a 40k note at most custodians runs another 30 to 60 basis points that nobody puts in the comparison.

What is the typical loan-to-value on the assets your notes are secured by, and are any of them cross-collateralized with debt at the entity level?

The assumption doing the most work in most of these comparisons is the denominator, and you've named it precisely. Idle time inside a custodial account is still time the money is under management, and the numerator, the stated coupon, does nothing to compensate for it.

The place I'd add pressure is on the syndication side of that comparison. A preferred share that deploys on day one and pays quarterly looks clean in the cycle analysis, but the capital return timeline is the variable the cycle comparison often treats as a given. If the preferred pays 7 percent and the exit comes in year five instead of year three, the effective annual return on the full hold period shifts, and unlike a note that pays off and gives you optionality, syndication capital is illiquid in the interim. The note has reinvestment friction. The preferred has reinvestment absence. Those are different problems with different carrying costs depending on what the next deployment looks like.

On the UDFI point, the analysis gets more complicated when the note itself is secured by a property carrying debt at the borrower level. The IRS treats UDFI exposure as turning on whether the IRA's asset is debt-financed, and a loan made by the IRA against an unencumbered asset is generally the cleaner position. Confirm the current UBIT thresholds and Form 990-T trust rate structure with a tax professional who works with SDIRAs, because the bracket where that 37 percent rate kicks in is inflation-indexed and moves.

The cycle yield framing you're describing is essentially a time-weighted return calculation applied to the full custodial period, and it's the right measure. The question it raises practically is whether the custodian's fee structure is fixed per transaction or scales with balance, because that changes the friction math on short-duration notes versus longer syndication holds.

What's the custodian fee model you're working with, direction letter per transaction or an annual asset-based fee?

The cycle-rate framing is the right one, and not enough people use it.

For anyone reading this who is new to the vocabulary: a self-directed IRA (an IRA where you choose the investment, not a brokerage) lets you hold things like private notes inside a retirement account. A private note is essentially a loan you make to a borrower, who pays you interest. A Roth IRA means you owe no tax on the growth. A "custodian" is the institution that holds the account and processes each transaction, and they charge fees for doing so.

The example above is showing something real. If $40,000 sits idle for six weeks at the start and four weeks at the end, that is ten weeks earning nothing. The stated 9 percent rate only describes the period the money was actually working. The full-cycle return, meaning what the money earned across every week it sat in the account, comes out lower.

The second point, about UDFI (Unrelated Debt-Financed Income), is one a tax professional needs to address for your specific situation, because the rules are precise and the consequences of getting them wrong matter. I would say that plainly rather than try to summarize it here.

One thing worth adding: the custodian fee structure varies a lot between providers. Some charge per transaction, some charge flat annual fees, and the difference can be meaningful when you are doing several short-cycle notes in a year. Asking a prospective custodian for a full fee schedule before you open the account is a reasonable step.

What type of assets are you currently deploying inside the account, or are you still at the comparison stage?