When you buy a rental or a commercial building, the IRS lets you write off its cost over time. This write-off is called depreciation. By default, the IRS spreads it over a long time: 27.5 years for a rental home and 39 years for a commercial building.
That is slow. A cost segregation study speeds it up. It breaks your building into parts. Some of those parts wear out faster than the walls and roof, so the law lets you write them off faster too.
The short version: a study moves big deductions from later years into your first year or two. More deductions now means a lower tax bill now, and more cash in your pocket today.
How a study works
An engineer studies your building and sorts it into groups based on how the tax code treats each part. The slow-life shell stays on the long schedule. But many parts qualify for much shorter lives:
- 5-year parts: carpet, appliances, cabinets, special wiring, and decorative lighting.
- 15-year parts: paving, sidewalks, fencing, landscaping, and outdoor lighting.
- 27.5 or 39-year parts: the building shell itself, like the frame, roof, and walls.
Once the engineer sorts the parts, you can claim the short-life deductions right away instead of waiting decades.
Why faster is better
A dollar of deduction today is worth more than a dollar of deduction in 30 years. You can use the savings now to pay down debt, buy another property, or grow your business. This is the time value of money, and a study puts it to work for you.
A study moves big deductions from later years into now, when they help you most.
It works even better with bonus depreciation. Under the OBBBA law, 100% bonus depreciation is permanent for property acquired and placed in service after January 19, 2025. That means you can deduct the full cost of qualifying short-life parts in year one. A study finds those parts so you can claim the full benefit.
What kinds of property qualify?
Almost any building you depreciate. That includes single-family rentals, duplexes, apartments, short-term rentals, hotels, restaurants, retail, office, medical, industrial, and warehouse space. Land itself is not depreciable, so the study works on the building and the site improvements.
A worked example
Numbers make this concrete. Say you buy a rental house for $500,000. The county says 20% of the value is land, so $100,000 is land and $400,000 is the building you can depreciate.
| No study | With a study | |
|---|---|---|
| Depreciable building cost | $400,000 | $400,000 |
| Moved to 5- and 15-year parts | $0 | $80,000 |
| First-year deduction | $14,545 | $91,636 |
| Tax saved in year one at 32% | $4,654 | $29,324 |
Without a study, the whole $400,000 sits on the 27.5-year schedule, so year one is about $14,545. With a study, $80,000 moves into 5- and 15-year classes that qualify for 100% first-year bonus depreciation, and the remaining $320,000 keeps depreciating normally. First-year deductions go from roughly $14,500 to roughly $91,600.
The 20% reclassification rate in this example is a common outcome, not a promise. A furnished short-term rental with heavy site work can run higher; a plain apartment with a bare lot runs lower. That is exactly what a study measures, and what our free calculator estimates for your own numbers.
Who it is for, and who it is not
A study pays off in some situations and not others. Being honest about both saves you money.
| Good fit | Poor fit |
|---|---|
| Building cost above roughly $200,000 | A small, low-cost property |
| You plan to hold it several years | You are selling within a year or two |
| You have income the deduction can offset | The loss would sit unused and suspended |
| Furnished, or lots of site work | Bare land-light building, little inside it |
| You are in a higher tax bracket | An unusually low-income year |
That third row is the one people miss. A deduction only lowers this year's tax if you can use it this year. Rental losses are usually passive, which means they cannot offset salary unless you qualify under the short-term rental rules or you have other passive income. Otherwise the deduction is real but waits.
What the process actually looks like
- Split land from building. Land never depreciates, so this comes first and caps everything after it.
- Inventory the components. Photos, measurements, and documents covering what is actually in and around the building.
- Cost each part. Either from your actual invoices or a recognized cost-estimating method.
- Classify each part into its recovery period, with a reason that holds up.
- Produce the schedules and filing forms, includingForm 3115 if you have owned the property more than a year.
You can see exactly what the finished product looks like: our full sample report is public, appendices included. Our fees are published too.
The honest limits
Three things a fair explanation has to say.
It is a deferral, not extra money. Total depreciation over the life of the building is the same either way. A study changes the timing, not the total. The benefit is real, because money now is worth more than money in 2050, but nobody is creating new deductions.
Selling brings some of it back. Faster depreciation lowers your basis, so a sale produces more gain, and the part tied to personal property is recaptured at ordinary rates instead of capital-gain rates. If you are selling soon, a study can cost you more than it saves.
The documentation is the deduction. A number without support is a liability. The IRS publishes what it expects a credible study to contain, which is why a real study includes photo evidence and cited authority rather than a percentage someone applied.
Already own the property?
You do not have to catch this in the year you buy. A study on a property you have held for years can claim all the depreciation you should have taken, as a single catch-up in the current year, using Form 3115 and a §481(a) adjustment. No amended returns needed.
Common questions
What is cost segregation in simple terms?
It is a study that splits your building into parts, so the parts that wear out faster can be written off faster. Instead of deducting the whole building over 27.5 or 39 years, you deduct the carpet, appliances, landscaping, and paving over 5 or 15 years.
Is cost segregation legal?
Yes. It applies the depreciation rules Congress wrote, and the IRS publishes an Audit Techniques Guide describing how to do it properly. Decades of court decisions define which components qualify.
How much does a study cost?
Ours start at $497 for a smaller residential property and are set by property value, not by your savings. The wider industry usually quotes $5,000 to $15,000. The full fee schedule is published here.
Does it work on a rental house, or only big commercial?
Both. Single-family rentals, short-term rentals, and small multifamily all work, and furnished short-term rentals are often the strongest cases because of everything inside them.
Do I need an engineer to do it?
No rule requires a licensed professional, though the classification and costing work is what makes a study hold up. We wrote honestly about doing it yourself.
Will a study trigger an audit?
A properly documented study is a normal, well-established tax position, not a red flag. What draws scrutiny is an aggressive allocation with no component detail behind it.
What is bonus depreciation's role?
Property with a recovery period of 20 years or less can be deducted in full in year one. The study identifies which parts those are.100% bonus is permanent again for property acquired and placed in service after January 19, 2025.
Next step:See your savings range in seconds for your property, or read is a cost segregation study worth it? to see if the math works for you.
This guide explains general tax ideas in plain words. It is not tax advice for your specific situation. The dollar figures are illustrative, not a projection for your property, and whether a deduction is usable this year depends on your own tax situation. Your study and tax positions are reviewed by a licensed tax professional. Always confirm the plan with your own advisor.