§1031 Carryover Basis Interaction With Reclassification: Sequencing Matters
Worked walkthrough on whether to commission a cost-seg study before or after a §1031 exchange — with carryover basis math and a 5-year horizon NPV.
§1031 Carryover Basis Interaction With Reclassification: Sequencing Matters
What you'll learn. How carryover basis under IRC §1031(d) propagates through to a cost-segregation reclassification on the replacement property, when to study the relinquished property vs. the replacement, and the dollar swing on a worked $1.2M exchange. This complements the §1031 hero article by quantifying the sequencing decision.
The core mechanic
IRC §1031(d) requires the replacement property's basis to be the relinquished property's adjusted basis, decreased by money received and increased by money paid plus gain recognized. The result is usually a carryover basis significantly lower than the replacement's purchase price. Cost segregation reclassifies a fraction of basis — so a lower basis reclassifies fewer dollars, full stop.
Treas. Reg. §1.168(i)-6 governs how MACRS recovery periods carry over post-exchange. The rule: replacement property is split into "exchanged basis" (carried over) and "excess basis" (new money paid). Each piece depreciates separately.
- Exchanged basis continues the relinquished property's recovery period and method (the replacement "steps into" the relinquished depreciation schedule).
- Excess basis is treated as newly acquired and gets fresh MACRS — including bonus depreciation if §168(k) applies.
The taxpayer can elect under Treas. Reg. §1.168(i)-6(i) to treat the entire replacement basis as newly placed in service — a §1.168(i)-6(i) election — which sometimes (rarely) helps.
Worked example — a 2026 exchange
- Relinquished: rental purchased March 2018 for $600,000 (land $100,000, building $500,000). Cumulative S/L depreciation through May 2026: $500,000 / 27.5 × 8.17 = ~$148,545. Adjusted basis: $600,000 - $148,545 = $451,455.
- Replacement: STR purchased June 2026 for $1,200,000 (land $240,000, replacement building $960,000)
- Exchange closes mid-May 2026, fully qualifying §1031 deferral. Boot: $0.
- Carryover basis: $451,455 — allocated $90,291 to land and $361,164 to building (using the relinquished allocation).
- Excess basis: $1,200,000 - $451,455 = $748,545 — allocated $149,709 to land and $598,836 to building.
Without electing §1.168(i)-6(i)
The exchanged-basis building ($361,164) continues the relinquished's 27.5-year schedule with ~19.3 years remaining and the original April 2018 placed-in-service convention applied prospectively. The excess-basis building ($598,836) starts fresh under 27.5-year mid-month convention from June 2026.
A cost-seg study run on the replacement property only can reclassify both pieces of basis in proportion to the engineering allocation:
- Combined building basis: $361,164 + $598,836 = $960,000
- 28% accelerable on STR (post-adjustments): $269,000
- Allocated to exchanged basis: $269,000 × ($361,164 / $960,000) = $101,202 - Allocated to excess basis: $269,000 × ($598,836 / $960,000) = $167,798
The excess-basis $167,798 of accelerable property is bonus-eligible because it's "acquired" in 2026 and §168(k)(2)(A)(ii) tests acquisition date. The exchanged-basis $101,202 is not bonus-eligible — Treas. Reg. §1.168(k)-2(b)(3)(iv)(B) excludes property whose basis is determined by reference to property previously placed in service. The exchanged-basis accelerable bucket only gets MACRS Tables A-1 / A-2 (200% DB or 150% DB) over the original recovery period from the relinquished property's placement date.
Year-1 deduction comparison
- Excess-basis bonus (5-yr + 15-yr): $167,798 × 100% = $167,798
- Exchanged-basis MACRS year-1 on $101,202: ~$20,200 (MACRS year-9 percentages on the 5-yr table are zero; the 15-yr exchanged basis still has remaining MACRS, generally 5.9%/yr through the late years). Practical: ~$5,500–$8,000 of year-1 deduction on the exchanged-basis accelerable bucket.
- Excess-basis building (post-bonus residual zero, S/L year 1 mid-month June): $598,836 - ($167,798 × $598,836/$960,000 = $104,580) = $494,256 / 27.5 × (6.5/12) = ~$9,743
- Wait — the cleaner pattern: bonus is on the accelerable buckets only, not the building. Let me restate. Year-1 deduction:
- Bonus on accelerable: $167,798 - Excess-basis building S/L mid-month: $598,836 / 27.5 × (6.5/12) = $11,809 - Exchanged-basis carryover MACRS (year-9 of original schedule): ~$13,000 - Plus exchanged-basis 5-yr/15-yr MACRS: ~$7,000
- Total year-1 deduction: ~$199,607
- Federal tax effect at 35%: ~$69,862
Comparison — pre-exchange study on the relinquished property
If the taxpayer had run a cost-seg study on the relinquished property in 2024 (year of acquisition + 6) before the exchange:
- Relinquished basis $500,000, ~22% accelerable on LTR = $110,000 of accelerable property
- 2024 was a 60% bonus year under TCJA phase-down
- Year-of-study deductions: ~$66,000 bonus + first-year MACRS = ~$72,000
- §481(a) catch-up filed via Form 3115 — ~$48,000 negative adjustment in 2024
Then the 2026 exchange happens. Carryover basis is now ~$451,455 - additional accelerated depreciation from 2024–2026 of ~$30,000 more than straight-line = ~$421,455 carryover.
The 2026 cost-seg study on the replacement now reclassifies on a smaller exchanged-basis pool ($421,455 × $960,000/$1,200,000 of building share = ~$337,164) — about $24,000 less of exchanged-basis allocable to accelerable. But the 2024 study already pulled forward ~$15,000 of NPV that the post-exchange study would have caught later anyway.
The sequencing recommendation
When the planned hold period on the replacement property is short (under 5 years), a study on the relinquished property pre-exchange tends to win — front-loaded deductions compound longer. When the planned hold period on the replacement is long (10+ years), the post-exchange study on the larger combined basis tends to win — more dollars to reclassify outweighs the carryover-basis bonus exclusion.
Engineering firms increasingly run dual studies — one on the relinquished property right before exchange, then a second on the replacement immediately after. Combined, they capture every available bonus dollar on every basis bucket. The economic justification holds when the combined accelerable basis exceeds ~$300,000.
§1245 recapture on the exchange
§1031(d) defers gain on the relinquished property — including the §1245 ordinary-recapture portion — to the replacement. The recapture potential travels with the carryover basis. When the replacement eventually sells in a fully taxable transaction, all accumulated §1245 depreciation across both properties recaptures as ordinary income. See the §1245 3-year flip math for the back-end mechanics.
Where the screening tool fits
Our feasibility estimator does not currently model the carryover-basis split. The current engine computes reclassification on the full purchase price minus land value — which is correct for a non-exchange acquisition but overstates the year-1 deduction on a §1031 replacement. Until that model is added, the practitioner should manually scale the engine's accelerable output by excess_basis / (excess_basis + exchanged_basis) to approximate the bonus-eligible portion. The exchanged-basis portion still gets MACRS but not §168(k) bonus.
Screen a 2026 replacement-property cost-seg before applying the exchange haircut →
Sources
- IRC §1031(d) — Basis of replacement property
- IRC §168(k)(2)(A)(ii) — Acquisition-date test for bonus eligibility
- Treas. Reg. §1.168(i)-6 — Like-kind exchange depreciation rules
- Treas. Reg. §1.168(i)-6(i) — Election to treat entire basis as newly acquired
- Treas. Reg. §1.168(k)-2(b)(3)(iv)(B) — Carryover-basis exclusion from bonus
- Rev. Proc. 2025-15 — §1031 procedural updates
- IRS Publication 544 — Sales and Other Dispositions of Assets
- IRS Form 8824 Instructions — Like-Kind Exchanges
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.