STR Cost Segregation: Year 1 vs Year 2 (Why Timing Matters Under §168)

The Bonus Depreciation Phase-Down (This Is the Whole Argument)

IRC §168(k) lets you deduct a percentage of qualifying property in the year it's placed in service, on top of regular MACRS depreciation. The TCJA set that percentage at 100% through 2022, then scheduled a step-down every year.

Acquisition + placed-in-service timing	Bonus % under §168(k)
Acquired after Jan 19, 2025 (any placed-in-service year)	100% (restored permanently by the mid-2025 law)
Acquired on or before Jan 19, 2025 · placed in service 2017 – 2022	100%
Acquired on or before Jan 19, 2025 · placed in service 2023	80%
Acquired on or before Jan 19, 2025 · placed in service 2024	60%
Acquired on or before Jan 19, 2025 · placed in service 2025	40%
Acquired on or before Jan 19, 2025 · placed in service 2026	20%

"Placed in service" is the key phrase — it's when the property is ready and available for use, not when you bought it. For an STR, that's usually when the listing goes live and you can accept bookings.

For property acquired on or before Jan 19, 2025, the year you place it in service locks in your bonus rate — placed in service December 2025 → 40%, drag the listing into January 2026 → 20%. That one-month decision is worth thousands. For property acquired after Jan 19, 2025, current law puts you at 100% either way — but "acquired" has its own rules (binding contracts count), so have your CPA confirm which side of the line you're on.

What Cost Seg Actually Reclassifies

Without cost seg, the whole building depreciates over 27.5 years (residential rental under §168(c)). Cost seg breaks the property into components with shorter recovery periods:

Asset class	Recovery period	Bonus-eligible?	STR examples
5-year property	5 years	Yes	Furniture, appliances, decorative lighting, carpets, blinds, TVs, kitchenware
7-year property	7 years	Yes	Outdoor furniture, office equipment, some tools
15-year property	15 years	Yes (Qualified Improvement Property)	Driveways, sidewalks, landscaping, fences, outdoor lighting, pool equipment
27.5-year property	27.5 years	No	Building structure (walls, roof, foundation, plumbing, electrical)

For a typical STR, cost seg studies commonly identify 20-35% of the depreciable basis as 5/7/15-year property. On a $500K building with $400K depreciable basis (subtracting land), that's $80K-$140K reclassified from 27.5 years to accelerated schedules.

The Year-1 Math That Actually Matters

Say you place an STR in service in 2026 with $400K depreciable basis. Cost seg identifies $100K as 5-year property (25% is realistic for an STR with a lot of furnishings).

Without cost seg:

• Year 1 depreciation: $400K ÷ 27.5 × (mid-month convention for month placed in service) ≈ $7-14K deducted

With cost seg · acquired after Jan 19, 2025 (100% bonus under current law):

• 5-year property: $100K × 100% bonus = $100K deducted fully in year 1
• 27.5-year remainder ($300K): standard depreciation ≈ $6-11K
• Total year-1 deduction: roughly $107K

Contrast: same property acquired on or before Jan 19, 2025, placed in service 2026 (20% bonus):

• 5-year property: $100K × 20% bonus = $20K bonus + regular MACRS on remaining $80K = ~$36K year-1 total on that bucket
• Total year-1 deduction: roughly $42-47K

Same property, same cost seg — which bonus regime the acquisition falls under changes the year-1 deduction by more than 2x. (All figures illustrative estimates.) That's the timing argument in one table.

What Happens If You Miss Year 1

Two paths if you didn't do cost seg in year 1:

Option A · Do it in year 2+ via Form 3115

The IRS allows a "change in accounting method" via Form 3115. You reclassify assets retroactively and take the entire missed depreciation as a §481(a) catch-up adjustment in the current year.

Catch: the bonus rate applied is the rate in effect for the year the property was placed in service — not the current year. Miss doing cost seg in 2022? File Form 3115 in 2026 and you still get the 100% bonus on that property.

This is genuinely powerful. If you have properties from prior years that never got cost seg, Form 3115 is often worth revisiting with a specialist.

Option B · Do it prospectively

Just do cost seg going forward. Year-1 depreciation is gone (unrecoverable at the higher bonus rate), and you take normal accelerated MACRS from the current year forward. Simpler paperwork than 3115 but leaves money on the table.

DIY Estimator vs Certified Study

DIY estimator (like RentReel's)

• Free or bundled with bookkeeping software
• Ballpark within ~15% of a real study for typical STRs
• Good for: pre-purchase modeling, deciding whether to hire a specialist, sanity-checking a specialist's numbers
• Not IRS-defensible on its own — no engineer walk-through, no photo documentation, no detailed asset breakdown

Certified cost seg study

• Cost: typically $2,500 – $8,000 depending on property value and complexity
• Includes an engineering site walk-through, photo documentation, detailed asset schedule, audit-defense support
• Deliverable is IRS-audit-ready
• Rule of thumb: any property over $300K basis + STR-loophole-qualified typically pays for the study in year-1 tax savings alone

Estimator first, specialist second. Run the DIY numbers to see if the potential savings justify the study fee. If the estimator says $30K+ in year-1 acceleration, a $5K certified study is a no-brainer. If it says $8K, probably not worth it.

Passive vs Non-Passive Trap

Cost seg by itself just creates a bigger passive loss on a passive rental — you can only deduct it against passive income. Useless for most operators.

Cost seg on an STR that qualifies for the loophole (avg stay ≤ 7 days + material participation) creates a non-passive loss. That deducts against W-2 income, business income, spouse's income — the good stuff.

So the sequence matters:

1. Verify avg stay ≤ 7 days on the property
2. Verify you can meet a material-participation test (see the 7 tests)
3. THEN do cost seg

Doing cost seg without step 1 or 2 just parks the loss until you have passive income to offset it.

Action List

1. List every property + placed-in-service year. Any property placed in service 2017-2024 that never got cost seg is a Form 3115 candidate — the bonus rate for that year still applies.
2. Run a DIY estimator on each candidate. Even a rough number tells you whether a specialist is worth the fee.
3. Confirm STR loophole qualification first. Cost seg on a passive rental just parks losses. Verify avg stay ≤ 7 days and material participation before spending.
4. Time future acquisitions carefully. A December purchase that gets listed in December vs January can shift you a full year of bonus rate.
5. Talk to a certified cost seg specialist. Not your general CPA — someone who does this full-time. Engineering-based studies are what hold up in audit.

Sources

• IRC §168 · Depreciation (including §168(k) bonus)
• Form 3115 · Application for Change in Accounting Method
• IRS Publication 946 · How to Depreciate Property
• IRS Publication 925 · Passive Activity Rules — for passive vs non-passive treatment
• Reg. §1.469-1T(e)(3) — STR loophole definition (avg stay ≤ 7 days)