Windham v. Commissioner: what a defensible log looks like

By Max Medvedev · 6 Aug 2026

Windham v. Commissioner, T.C. Memo 2017-68, is one of the wins, and it is the most useful case here for anyone building a record. The taxpayer kept a credible log as the work happened, backed it with independent documents, and did it alongside a part-time job. The record held, and material participation was proven.

What happened

The taxpayer kept a participation record in real time rather than assembling one at filing, and did not rest the case on the record alone — independent documents corroborated what the log said.

The other fact worth noticing is the part-time job. Outside obligations were part of the picture, and they did not defeat the position.

What the court held

Material participation was proven. The log was credible, and the corroboration is what made it credible.

The standard being satisfied here is the lenient one. Reg. §1.469-5T(f)(4) says participation may be established "by any reasonable means," and that "contemporaneous daily time reports … are not required" — appointment books, calendars, and narrative summaries can suffice. Birdsong v. Commissioner, T.C. Memo 2018-148, is the companion case on that point: detailed spreadsheets plus credible testimony met the "reasonable means" bar.

But the regulation is the floor, not the bar. The Tax Court routinely refuses reconstructions built after the year is over — Moss v. Commissioner, 135 T.C. 365 (2010), is the seminal line, that the regulations "do not allow a post-event ballpark guesstimate," and Sezonov v. Commissioner, T.C. Memo 2022-40, applied exactly that to a short-term rental with no real-time log. Windham is the same standard viewed from the winning side: the record satisfied a lenient regulation because it was built the strict way.

The tell

The deciding behaviour in the losses is always something the log did. In Windham it is something the log pointed at.

Corroboration is the mechanism. A log is the taxpayer's own account, and an account that cites nothing outside itself is an assertion no matter how detailed it is. A log that lands next to booking-platform records, timestamped guest message threads, cleaner and contractor invoices, calendar entries, supply receipts, and bank activity is a different object — every entry has a second source that was created by someone else, for another purpose, at the time.

Credibility, once established, buys margin. This is the part owners underrate. A record the court believes gets the benefit of the doubt on its gaps: in Leyh v. Commissioner, T.C. Summ. Op. 2015-27, a clean real-time log earned the taxpayer that benefit on travel time that had been left out. Compare that with the losses, where an incredible total was discarded whole and the genuine hours inside it went down with the padding. The same imperfection reads as an honest omission in one record and as evidence of construction in the other. Which one you get is decided long before the imperfection comes up.

The other job cut the right way. A part-time job alongside the rental did not sink the position, and a full-time dental practice did not sink Zarrinnegar. The examiner's feasibility question — are these hours reasonable in light of other obligations — is answerable, and a record that shows the work fitting into real weeks answers it. What loses is a total that could not have fit into anyone's week.

What this means for your records

The log is the spine and corroboration is what makes it stand up. Practically, that means the evidence has to be attached at the moment of the entry, not gathered later — which is the only real difference between the Windham shape and the Sezonov shape.

What a defensible file pairs with each entry:

• Booking-platform exports — they prove the average-stay math (total nights ÷ number of reservations) and date every guest arrival and departure.
• Guest message threads — timestamped, and they tie directly to logged communication hours.
• Cleaner and contractor invoices and schedules — these do double duty, evidencing your coordination work and documenting how many hours the other individual worked, which is the second leg of the 100-hour test.
• Calendar entries, pricing changes, supply receipts, maintenance tickets, bank records, timestamped photos — the ordinary residue of running the place.
• Mileage, only where the travel was integral to the work performed — travel is the fragile category; the audit guide says it generally should not be considered.
• The §280A personal-use log — owner and family nights, plus the fair value of any discounted stays, showing the greater-of-14-days-or-10% line was not crossed.

Two more things travel with the Windham shape. Document your other job's hours, because the feasibility question is asked in the opening interview, not at the end. And keep the participation log for seven years — the ordinary statute of limitations runs three years, six where income is understated by more than 25%, and basis, depreciation, and cost-seg records have to survive until three years after the sale, because they set the recapture math.

None of that is a filing-season project. Everything in a file like this exists because it was captured while the work was happening, which is the entire argument for logging in real time when the regulation, read literally, would let you reconstruct.

Build the record the wins are built on

The shape is copyable: real-time entries, sized to the task, each pointing at a document someone else created. Run your year through the estimator to see which participation test your countable hours reach and who you have to out-work to get there.

The full method sits in how to prove your short-term rental hours, and the average-stay gate that has to clear first is in the 7-day test.