Standard depreciation spreads your building's cost evenly over 27.5 years. Cost segregation breaks the building into components — carpet, appliances, cabinets, site improvements — that the tax code lets you depreciate over 5, 7, or 15 years instead, pulling large deductions into the early years of ownership. It doesn't create deductions; it moves them forward, and moved- forward tax savings are worth real money.
How it works
An engineering-based study (the defensible kind) inspects the property and allocates the purchase price: typically 20–30% of a residential rental's improvement value lands in short-life buckets — flooring and appliances (5-year), certain fixtures (7-year), landscaping, fencing, and paving (15-year). Bonus depreciation, when in effect, lets some or all of those short-life amounts deduct in year one; the percentage has been changing year to year, so current-law numbers are a CPA question.
What it costs and when it pays
Studies for small residential properties run roughly $1,500–$5,000 (larger commercial studies more). The value scales with your basis, your tax bracket, and — critically — your ability to USE the losses now: passive- activity limits can suspend the very deductions you paid to accelerate. Best candidates: recently purchased or built properties with $300,000+ of improvement basis, owners with passive income to offset or real-estate- professional status, and a multi-year hold ahead. You can also do a study years after purchase and catch up the missed depreciation in one year without amending returns.
Worked example
A $500,000 eightplex ($400,000 improvement basis) gets a $3,500 study that reclassifies 25% ($100,000) into short-life buckets. Even without bonus depreciation, first-five-year deductions rise by roughly $12,000–$15,000 per year versus straight-line; at a 32% marginal rate that's about $4,000–$4,800 of annual tax deferred forward. With bonus depreciation in effect, much of the $100,000 could deduct immediately — a five-figure year-one tax reduction against a $3,500 fee, IF the owner can absorb the loss under the passive rules.
When this rule of thumb breaks
Acceleration is deferral, not forgiveness: short-life depreciation recaptures at sale — often at ordinary rates rather than the 25% cap — so a quick sale can claw back much of the benefit (a 1031 complicates but can preserve it). Owners who can't use passive losses just build a bigger suspended pile. Cheap "residential calculator" studies without engineering support invite audit problems. And on a small basis the fee eats the benefit. Run the break-even with a CPA before commissioning anything.