Free Feasibility vs. Paid Engineering Study: Which Do You Need?
Honest comparison of a free cost-seg feasibility estimator vs. a paid engineering study. What each produces, what each costs, and where each one fits.
Free Feasibility vs. Paid Engineering Study: Which Do You Need?
What you'll learn. What a feasibility estimate actually produces, what a paid engineering study adds, where each one fits, and how property owners typically use them in sequence rather than as substitutes.
The two products are not the same thing
A common first-time confusion: "If I run the free calculator, do I still need to pay for a study?" The answer depends on what you intend to do with the result.
| | Feasibility estimate (free) | Engineering study (paid) | | --- | --- | --- | | Produced by | Algorithm using IRS ATG percentages | Licensed engineer or qualified CPA | | Inspection | None — questionnaire only | On-site inspection of building components | | Output | Screening Year-1 tax-effect estimate | Detailed asset reclassification report | | Filing weight | Cannot be relied on under Circular 230 | Designed to support the tax return | | Typical cost | $0 | $3,000–$8,000 (residential), more for commercial | | Time to complete | About 60 seconds | 4–12 weeks | | Typical use | Decide whether to commission a study | Support the actual return filing |
What the free feasibility estimate does
The TaxProtestTx feasibility estimator runs the same conceptual math as a paid study, using simplified heuristics:
- It applies base reclassification percentages from the IRS Cost Segregation Audit Techniques Guide Chapter 7.2 (5–15% personal-property reclass for 1–4 unit residential, higher for commercial / hotel / restaurant).
- It bumps those base percentages based on property-specific features the property owner enters (pool, custom kitchen, fencing length, lot size).
- It applies the current-year IRC §168(k) bonus rate per the OBBBA timeline.
- It surfaces the §469 passive-activity-loss gate and the §1245 recapture warning where they fire.
- It produces a 10-year depreciation comparison and a §481(a) catch-up estimate for prior-year acquisitions.
What the calculator output is: a screening number to decide whether the math is in the neighborhood. Directionally useful. Not return-ready.
What it explicitly is not: a deliverable you can rely on under Treasury Circular 230. The output cannot substitute for an engineering study on an audit.
What a paid engineering study adds
A full engineering study typically includes:
- On-site inspection. A licensed engineer walks the property and documents components — flooring type, cabinetry construction, fixture quality, landscaping detail, parking-lot composition.
- Cost segregation report. A formal deliverable with photographs, asset-by-asset basis allocation, MACRS class assignments, and supporting documentation under the IRS Cost Segregation Audit Techniques Guide.
- Engagement letter and engineer credentials. The report names the responsible engineer or CPA, their license number, and the methodology used. If audited, this is the foundation of the defense.
- Defense support. Most engineering firms include some level of audit support if the IRS challenges the allocation. Terms vary.
The deliverable is the report. The report is what the property owner's CPA cites on the return — typically Form 4562 Part III for the year of acquisition or Form 3115 with a §481(a) adjustment for a prior-year look-back.
How accurate is the free screening compared to a study?
A real engineering study will typically land within 10–25% of our screening number on a 1–4 unit residential property. Higher when the engineer finds detail items the questionnaire missed (utility allocations, partial-asset dispositions on prior renovations). Lower when the engineer rejects items the screening counted.
The screening is calibrated down from common engineering-firm marketing claims. Firm landing pages quoting "20–30% reclassification" usually combine 5-year and 15-year classes and select on properties where a study made sense. The IRS ATG Chapter 7.2 numbers — what we use — are 5–15% for personal property on residential rentals. We hold to the more conservative range to avoid systematic over-promising.
Three scenarios — which one fits
Scenario A: $300,000 single-family rental, 24% bracket, planning a 7-year hold
The screening estimate runs in 60 seconds. If the result lands "above threshold" (Year-1 tax effect ≥ $5,000), the property owner has the basis to commission a study — paying $3,000–$5,000 to capture an estimated $5,000–$15,000 Year-1 federal tax effect, with most of the benefit captured in the year of acquisition.
If the result lands "near threshold" ($2,000–$5,000), the math is closer. A CPA conversation typically decides whether the engineering fee pencils.
If the result lands "below threshold" (under $2,000), a study likely costs more than it saves in Year 1. The property owner can revisit if facts change (renovation, REPS qualification, higher tax bracket).
Scenario B: $1.2M commercial building, 35% bracket, indefinite hold
The screening output will almost certainly land "above threshold" by a wide margin. The decision isn't whether to commission a study but which firm to engage. The screening is useful as a pre-quote — property owners often share the screening output with prospective engineering firms to set expectations.
Scenario C: $400,000 long-term rental purchased in 2022, never studied
This is the §481(a) look-back scenario. The screening computes the catch-up adjustment — what the property owner should have deducted under cost-seg over 2022–2025, less what was actually claimed under straight-line. The catch-up flows into the current year via Form 3115.
For a 2022 purchase, four years of missed acceleration plus 100% bonus from the original placement year often makes the look-back catch-up larger than a fresh-acquisition Year-1 figure. Worth screening before deciding whether to engage an engineering firm for the look-back study.
Try a 2024 §481(a) look-back screening →
How property owners use them together
The standard sequence is feasibility → CPA conversation → engineering study → return, in that order:
- 1. Run the feasibility screening with actual property details.
- 2. Share the output with the CPA. Discuss bracket, REPS posture, holding-period plans.
- 3. If the CPA agrees the math pencils, engage an engineering firm.
- 4. Engineering firm produces the formal study.
- 5. CPA files the return citing the study.
The free feasibility step exists to prevent property owners from spending $3,000–$8,000 on a study that wouldn't have produced enough Year-1 benefit to justify the fee. It does not replace the study. It decides whether the study is worth commissioning.
When the screening is enough
For a low-basis property where the screening lands clearly "below threshold," the screening output may be enough — the property owner concludes that a paid study isn't worth pursuing this year. That decision is documented by the screening, the property continues on the standard 27.5-year (or 39-year) straight-line depreciation, and the question can be revisited in a future year if circumstances change.
The screening is never enough to actually file an aggressive position on the tax return. For that, the engineering study is the deliverable that bears the weight.
Run a feasibility screening → · Read the calculator walkthrough →
Sources
- IRS Cost Segregation Audit Techniques Guide
- IRS Cost Segregation Audit Techniques Guide Chapter 7.2 — Industry-Specific Guidance: Residential Rental
- Treasury Circular 230 — Practice before the IRS
- Rev. Proc. 2024-23, DCN 7 — Automatic accounting-method change for cost-segregation §481(a) catch-up
- Texas Occupations Code Ch. 901 — CPA practice scope (informs the distinction between a feasibility-screening tool and a cost segregation study)
Disclaimer. This tutorial describes general federal tax concepts. TaxProtestTx (Nought Labs LLC) is a feasibility-screening tool, not tax advice or a cost segregation study. Calculator output cannot be relied on under Treasury Circular 230. Consult a qualified CPA, EA, or attorney before filing. Results are not guaranteed.