How Bonus Depreciation and Cost Segregation Work Together (With Real Numbers)

Cost segregation and bonus depreciation are each powerful on their own. Combined, they produce first-year deductions that most investors find hard to believe until they see the math. This article walks through exactly how the two strategies interact — step by step — using a real STR property at multiple price points.

The Role Each Strategy Plays

Cost segregation is the analysis that identifies which components of your property can be assigned to shorter depreciation lives. Without cost segregation, the entire building (minus land) sits in the 39-year class. A cost seg study moves 25–40% of the improvement value into 5-, 7-, and 15-year classes — but without bonus depreciation, those faster-depreciating assets still spread their deductions over their recovery period.

Bonus depreciation is the mechanism that converts the reclassified assets into immediate deductions. Under §168(k), qualifying assets (5-, 7-, and 15-year property) are deducted 100% in year one. Without cost segregation, there's little qualifying property to apply bonus depreciation to — just separately purchased furnishings and appliances. Without bonus depreciation, cost seg still accelerates deductions but spreads them over multiple years.

Step-by-Step Walkthrough: $550,000 Airbnb

Let's work through a complete example. Michael buys a furnished lakefront cabin for $550,000 in October 2025. The property is placed in service in November 2025 after minor repairs.

1. Step 1 — Establish depreciable basis. The land is appraised at $82,500 (15%). Depreciable improvement basis: $467,500.
2. Step 2 — Cost segregation study. Abode's study identifies: $98,175 (21%) as 5-year personal property (furniture, appliances, lighting, window treatments); $46,750 (10%) as 15-year land improvements (deck, dock, landscaping, outdoor furniture); $322,575 (69%) as 39-year building.
3. Step 3 — Apply bonus depreciation. 5-year property: $98,175 × 100% = $98,175 deducted in 2025. 15-year property: $46,750 × 100% = $46,750 deducted in 2025. Total bonus depreciation year-1: $144,925.
4. Step 4 — Regular MACRS on remaining basis. 39-year property: $322,575 ÷ 39 = $8,271/year using straight-line (mid-month convention applies in year 1, so roughly $6,893 for partial year).
5. Step 5 — Add operating expenses. Mortgage interest: $24,000. Insurance: $3,600. Platform fees: $4,200. Repairs and maintenance: $3,800. Total operating expenses: $35,600.
6. Step 6 — Calculate net income/loss. Gross rental income: $52,000. Less: depreciation ($144,925 + $6,893 = $151,818). Less: operating expenses ($35,600). Net loss: ($135,418).
7. Step 7 — Apply through STR loophole. Michael materially participates (480 hours logged). Average guest stay: 4.2 days. Loss is non-passive → offsets Michael's W-2 income of $380,000. At 35% marginal rate: $47,396 in federal tax savings in year one.

Comparison: With and Without the Full Stack

The full stack — cost seg + 100% bonus depreciation + STR loophole — generates 11x more federal tax savings in year one than straight-line depreciation alone.

What Happens in Years 2–5

After the bonus depreciation is fully claimed in year one, the 5-year and 15-year assets have $0 remaining basis. Only the 39-year building component continues to depreciate at $8,271/year. This means year-two total depreciation drops significantly — from $151,818 to roughly $8,271 in year two (assuming no new capital improvements).

This "cliff" is entirely expected and planned for. The strategy front-loads deductions. Years 2–5 will likely show taxable income from the property unless new cost segregation opportunities arise (capital improvements, additional property acquisitions, or a retroactive study on a recently purchased second property).

Multiple Properties: Stacking the Effect

Many STR investors who experience the year-one benefit acquire additional properties in subsequent years to maintain the depreciation stack. Buying one new STR per year and doing a cost seg study on each creates a recurring stream of large first-year deductions that offsets growing W-2 income. This is a deliberate portfolio strategy — not a coincidence.