# What Reddit asks about cost segregation, answered with sources The cost segregation questions that keep coming up on Reddit and other forums, answered in plain words from IRS publications, the Code and the Tax Court. ## Short answer Type "cost segregation reddit", "cost segregation study reddit" or "bonus depreciation reddit" into a search engine and you get years of threads on r/realestateinvesting, r/tax, r/Accounting, r/AirBnB and r/Fire, most of them asking the same dozen questions: is it real, is it worth it, can I use the loss against my salary, what happens when I sell, is my Airbnb different, who should do it, and is a cheap online study legitimate. The answers below are ours, not Reddit's, and each one is tied to an IRS publication, the Code or a court decision listed under Sources. Where a question depends on facts only your tax adviser knows, we say so. This page is a map: each answer links to a longer article that goes into the rules. It is general education, not tax advice. ## "Is cost segregation actually legal, or a loophole?" It is neither a loophole nor a trick. Tax law already assigns different recovery periods to different kinds of property: land is not depreciated, residential rental buildings are recovered over 27.5 years, nonresidential buildings over 39, land improvements over 15, and items like appliances, carpeting and furniture over 5. A study documents which parts of a purchase fall into which class. The practice traces to the Tax Court's 1997 decision in Hospital Corporation of America, and the IRS publishes an Audit Techniques Guide telling its examiners how to review a study. What the IRS guide does not accept is a study built on guesses that does not reconcile to the real cost. More in [What a cost segregation study does](/articles/what-a-cost-segregation-study-does). ## "Is cost segregation worth it reddit" — the question behind the question The honest answer is "it depends," and the things it depends on are knowable before you spend a dollar: | It depends on | Why | |---|---| | The depreciable basis | The timing benefit has to exceed the study's fee after tax | | What the property contains | Furnished units, site work and equipment give a study more to find than a bare structure on a small lot | | Whether you can use the deduction this year | Rental losses are generally passive; the special allowance and real estate professional status are the exceptions | | Your holding period | Recapture at sale can undo a benefit taken shortly before | | Your state | Many states do not follow federal bonus depreciation | A study can be entirely accurate and still not help you this year. Ask your adviser the five questions above first. More in [Is cost segregation worth it?](/articles/is-cost-segregation-worth-it). ## "Can I use the loss against my W-2 income?" Usually not, unless one of two exceptions applies. Rental real estate losses are generally passive. Taxpayers who actively participate may deduct up to $25,000 of rental loss against other income, phased out between $100,000 and $150,000 of modified adjusted gross income. Taxpayers who qualify as real estate professionals, meaning more than half their personal services and more than 750 hours in real property trades or businesses in which they materially participate, are not subject to the passive limitation for those activities. Everyone else gets a suspended loss that carries forward. More in [Why a deduction is not a refund](/articles/why-a-deduction-is-not-a-refund). ## "What is the STR loophole everyone talks about?" The "STR loophole reddit" threads refer to a rule in the passive activity regulations, not a loophole: an activity is not a rental activity if the average period of customer use is seven days or less, or thirty days or less where significant personal services are provided. Such an activity is a trade or business, and its losses are nonpassive only if the owner materially participates under the seven tests, for example more than 500 hours, or more than 100 hours and at least as much as anyone else. Two other rules matter: a short-term rental may be 39-year nonresidential property because transient units are not dwelling units, and personal use beyond the greater of 14 days or 10 percent of rental days limits deductions. All of it turns on records. More in [Short-term rentals and cost segregation](/articles/short-term-rentals-and-cost-segregation). ## "Is bonus depreciation back to 100 percent?" For qualified property acquired after January 19, 2025, yes, and permanently, under the 2025 tax law, with a one-time transition election of 40 percent (60 percent for certain long-production-period property) for the first tax year ending after that date. Property acquired on or before January 19, 2025 stays on the old phase-down. Bonus depreciation applies to the 5-, 7- and 15-year property a study identifies, not to the 27.5- or 39-year building. The acquisition date, including the binding-contract rule, decides which regime applies. More in [Bonus depreciation and cost segregation after the 2025 law](/articles/bonus-depreciation-and-cost-segregation). ## "What happens when I sell? Do I pay it all back?" Not "back," but the tax arrives. Depreciation on the reclassified 5-, 7- and 15-year property is recaptured as ordinary income; depreciation on the building is unrecaptured section 1250 gain taxed at up to 25 percent. Section 1245 recapture is recognized in full in the year of sale even on an installment sale. Skipping depreciation does not avoid it, because basis is reduced by depreciation allowed or allowable either way. The trade is earlier deductions now against some tax at a higher rate later; the holding period decides whether it is a good trade. More in [Depreciation recapture after cost segregation](/articles/depreciation-recapture-after-cost-segregation). ## "I've owned the building for years. Too late?" Generally no. A study on a building already in service is applied through a change in accounting method on Form 3115 with the current return, with a section 481(a) catch-up adjustment, rather than by amending old returns. Automatic changes carry no user fee. The catch-up uses the rules in force when the property was placed in service, not today's bonus rate, and it is generally unavailable in the year you sell. More in [Look-back studies and Form 3115](/articles/look-back-cost-segregation-and-form-3115). ## "Who should do the study: engineer, CPA, or the $500 online one?" The IRS prescribes no qualifications for preparers. Its guide says a preparer's expertise affects quality, that engineering-based studies are generally more reliable, and that a quality study identifies the preparer and contains documentation, a legal analysis for classifications, unit costs and take-offs, an asset list and a reconciliation to actual cost. A questionnaire product with none of those is a percentage, which the guide treats as the least reliable approach. Verify any credential with the body that issued it and read a redacted sample against the guide's list. More in [Who is qualified to perform a cost segregation study?](/articles/who-is-qualified-to-perform-a-cost-segregation-study) and [How to hire a cost segregation practitioner](/articles/how-to-hire-a-cost-segregation-practitioner). ## "How do I split land from building?" By fair market value at purchase, using the appraisal, the purchase agreement and market evidence; when values are uncertain, Publication 551 permits allocation by the assessor's values. A land percentage from memory is not a method, and the land line is the first thing a reviewer checks because every later number depends on it. More in [Land and building allocation](/articles/land-and-building-allocation). ## "Does a cost seg study increase my audit risk?" No public IRS statement supports that claim, and this page makes no claim either way. What the IRS publishes is what its examiners request if a return with a study is examined: the complete study, the workpapers, the construction documents and the preparer's qualifications. The quality of the study is the variable you control. ## "Is my single-family rental big enough?" The rules apply to any depreciable rental building. Whether a study is worth its fee on a small house depends on the basis, the personal property and land improvements present, whether you can use the deduction, and how long you will hold. Vendors quote thresholds; those are rules of thumb. More in [Cost segregation for residential rental property](/articles/cost-segregation-for-residential-rental-property). ## What people ask on Reddit and other forums This whole page is that section, so here are the four questions that come up on r/realestateinvesting and r/tax after the ones above have been answered. **"My CPA says don't bother. The cost seg firm says I'll save $30k. Who is right?"** Possibly both. The firm can estimate what a study would find; only your adviser can say what it would do on your return, including the passive activity rules and your state. Ask the firm for its assumptions and ask the adviser to model them. **"Can I do my own study?"** Legally yes. Practically it has to contain the elements the IRS guide lists and survive the same requests from an examiner. Most owners cannot produce that file alone. **"Should I do it before or after my first tax year?"** Talk to the adviser before you buy. The acquisition and placed-in-service dates, the elections and the passive activity position are all easier to plan than to repair. **"Where can I verify that someone is certified?"** With the issuing body. NBCSS credentials are checked at the public verification page; membership is not certification, and no credential is approved by any government agency. ## Questions people also ask ### What subreddits discuss cost segregation? Mostly r/realestateinvesting, r/tax, r/Accounting, r/AirBnB and r/Fire, with career threads on r/civilengineering. This page does not quote or link individual threads; it answers the questions they raise from primary sources. ### Why does NBCSS answer Reddit questions? Because the questions are good and the answers in the threads are uneven. NBCSS is a professional membership organization for cost segregation practice; publishing sourced answers to the questions people actually ask is part of its purpose. ### Are these answers tax advice? No. They are general education with sources. Every one of them depends on facts your adviser holds. ### Can I send you a Reddit thread to answer? Yes. Use the corrections address on the articles page. Threads we answer are cited in the article that addresses them. ### Where do I start if I want the full picture? With [What a cost segregation study does](/articles/what-a-cost-segregation-study-does), then [Why a deduction is not a refund](/articles/why-a-deduction-is-not-a-refund), then the article for your property type. ## Sources - https://www.irs.gov/publications/p946 — IRS Publication 946 (2025), How To Depreciate Property: Chapters 1 and 4. - https://www.irs.gov/publications/p925 — IRS Publication 925 (2025), Passive Activity and At-Risk Rules: rental activity exceptions; material participation tests; special allowance; real estate professional. - https://www.irs.gov/newsroom/treasury-irs-issue-guidance-on-the-additional-first-year-depreciation-deduction-amended-as-part-of-the-one-big-beautiful-bill — IR-2026-06 (January 14, 2026), bonus depreciation guidance and transition election. - https://www.irs.gov/publications/p544 — IRS Publication 544 (2025), Sales and Other Dispositions of Assets: Chapters 3 and 4. - https://www.irs.gov/publications/p537 — IRS Publication 537 (2025), Installment Sales: Depreciation Recapture Income. - https://www.irs.gov/instructions/i3115 — Instructions for Form 3115, Application for Change in Accounting Method. - https://www.irs.gov/pub/irs-pdf/p5653.pdf — IRS Publication 5653, Cost Segregation Audit Techniques Guide (Rev. 2-2025): Chapters 3, 4 and 5. - https://www.law.cornell.edu/uscode/text/26/168 — 26 U.S.C. §168(e)(2)(A). - https://www.irs.gov/publications/p551 — IRS Publication 551 (Rev. December 2024), Basis of Assets. - https://www.leagle.com/decision/1997130109btc211129 — Hospital Corporation of America v. Commissioner, 109 T.C. 21 (1997). ## Related reading - [What a cost segregation study does](/articles/what-a-cost-segregation-study-does) - [Is cost segregation worth it? A decision checklist](/articles/is-cost-segregation-worth-it) - [Why a deduction is not a refund](/articles/why-a-deduction-is-not-a-refund) - [Short-term rentals and cost segregation](/articles/short-term-rentals-and-cost-segregation) - [Who is qualified to perform a cost segregation study?](/articles/who-is-qualified-to-perform-a-cost-segregation-study) - [Depreciation recapture after cost segregation](/articles/depreciation-recapture-after-cost-segregation) - [Find a practitioner in the NBCSS directory](/directory) --- Canonical: https://nbcss.org/articles/cost-segregation-questions-from-reddit Published: 2026-09-25 · Last content change: 2026-09-25 Not professional advice: general educational information from the National Board of Cost Segregation Specialist (NBCSS); not accounting, tax, legal, financial, investment or engineering advice. Verify with a licensed CPA, enrolled agent, attorney or other qualified adviser before acting.