Cost segregation study: how it works in 2026

By Preston Seo, founder of Legacy Investing Show. Last reviewed October 22, 2026. Change log: Oct 22, 2026 added a sample study, the payoff test on a sale, who does a study, and the Form 3115 filing steps. Oct 6, 2026 rewrote the page for 2026 law, replaced the savings claims with a worked example, and added the passive loss check, video, and IRS links.

What is cost segregation?

When you buy a rental, the tax default puts almost the whole price, minus land, into one asset: a 27.5 year residential building or a 39 year commercial building. You deduct a small slice each year.

A building is not one thing, though. It has carpet, appliances, cabinets, special wiring, and a parking lot. The tax code gives many of those parts shorter lives. A cost segregation study is an engineering review that finds them and assigns each one its proper class:

• 5 year property: appliances, carpet, furniture, and some fixtures in a rental.
• 7 year property: some furniture and equipment, mostly in commercial buildings.
• 15 year property: land improvements such as driveways, sidewalks, fencing, landscaping, and outdoor lighting.
• 27.5 or 39 year property: the building shell, roof, framing, and core systems that stay.

Land never depreciates. The IRS explains what a good study looks like in its Cost Segregation Audit Techniques Guide, Publication 5653. The best studies use a detailed engineering approach with a line-by-line asset list.

Why does cost segregation matter more in 2026?

Every part with a life of 20 years or less qualifies for bonus depreciation. The One Big Beautiful Bill Act made the bonus rate 100% and permanent for qualified property acquired after January 19, 2025. The IRS explained the rules in Notice 2026-11.

So in 2026 a study does two things at once. It moves part of the building into short-life classes, and then bonus depreciation writes all of those parts off in the first year. Before the 2025 law, the bonus rate had fallen to 40% for 2025 and was set to hit 20% in 2026. Property under a binding contract on or before January 19, 2025 still uses that old schedule.

Who is cost segregation right for?

It usually fits when all of these are true

• You own, or are about to buy, a building with a depreciable basis of about $400,000 or more.
• You can use the loss this year. That means the short-term rental loophole, real estate professional status, passive income from other rentals, or business income if it is a business property.
• You are in the 24% bracket or higher, so the deduction is worth the fee.
• You plan to hold the property for years, not months.

Who this does not work for

• A W-2 earner with a long-term rental and no way to use passive losses. The loss is suspended and carried forward. It is not lost, but it does nothing this year.
• Small properties. On a building worth much under $400,000, the fee can eat most of the first-year benefit.
• Anyone who plans to sell in a year or two. The short-life parts come back as ordinary income through Section 1245 recapture.
• People in a low bracket now who expect a higher one later. You would deduct at a low rate and pay back at a high one.
• Owners in states that do not follow federal bonus depreciation, unless they run the state return as a second column.

What does a study do to the first-year deduction?

This is an example, not a forecast. It follows the duplex example in Preston's video below. Every number is an assumption.

The last row is the one most sales pitches skip. A study creates a large deduction. Whether it saves tax this year depends on the passive loss rules. Check that first, then pay for the study. Run your own numbers with the cost segregation savings calculator and the bonus depreciation estimator.

Sample cost segregation study: a worked example

Here is what a simple study looks like on a single-family short-term rental, step by step. A real study uses your own closing statement, records, and a site visit.

Step 1: The property and the assumptions

Step 2: What the study moved

The study reclassified $150,000, or 25% of the depreciable basis. That is inside the 20% to 30% range studies often find on home-style rentals.

Step 3: First-year depreciation under the 2026 rules

The contract was signed after January 19, 2025, so the 5, 7 and 15 year parts get 100% bonus depreciation. The building stays on straight-line depreciation over 27.5 years. Some preparers use 39 years for a short-term rental with average stays of 7 days or less, so ask your CPA which life fits your property. A building placed in service in April gets 2.576% in the first year under the mid-month table in IRS Publication 946.

Step 4: The tax effect

The study did not create new deductions. Total depreciation over the life of the property is still $600,000. The study pulled $146,136 of it into the first year. If the loss were passive and the owner had no passive income, the first-year value would be $0, and the loss would carry forward.

What a real study report includes

• A description of the property, the site visit, and the method the engineer used.
• The split between land and building, with support for it.
• An asset list with each item, its cost, and its tax class.
• A summary by class, like the table in step 2.
• A depreciation schedule your preparer can enter on Form 4562.
• For a property you bought in an earlier year, the catch-up amount for Form 3115.
• Photos and a list of the documents used.

IRS Publication 5653 treats a detailed engineering approach, built from actual cost records or a detailed cost estimate, as the most reliable kind of study.

When does a cost segregation study pay off?

A study pays off when three things line up. You can use the loss now. The tax value is several times the fee. And you keep the benefit long enough. To see the last part, here is the same sample property sold after five years, in April 2031, for $900,000 with $54,000 of selling costs. The owner is still in the 37% bracket and pays 20% on long-term capital gain.

Over the five years, the study added $122,729 of deductions, worth about $45,410 at 37%. The sale then cost $46,522 more in tax. In this case the dollars about wash out. What the owner gained was the use of about $54,000 in the first year, with no interest, for five years.

The result gets better for the owner when:

• You hold much longer. The later the sale, the longer you keep the money.
• You sell through a 1031 exchange. A valid exchange defers recapture into the next property.
• You hold until death. Under current law, heirs get a stepped-up basis and the recapture goes away.
• Your rate is lower in the year you sell. You deducted at 37% and pay back at a lower rate.
• The 5 year items are worn out when you sell. Section 1245 recapture is limited to the gain on those items. If the sale price assigned to them is low and you can support it, the ordinary slice shrinks.

Run your own sale with the depreciation recapture calculator. It splits the gain into the ordinary-rate slice, the 25% slice, and capital gain.

What does our own data show?

Preston built a portfolio of about 40 long-term rental units in his first two and a half years of investing, while he still had a full-time software sales job. A long-term rental owned by someone with a full-time job is passive. That is why our plans pair cost segregation with a way to use the loss, rather than treating the study as the goal.

Of the 61 wealth plans we published between August 2025 and April 2026, 34 mention cost segregation. One plan dated April 11, 2026 modeled a $500,000 to $600,000 short-term rental with a target first-year loss of $150,000, which is inside the 20% to 30% range a study often finds on that kind of property. Plans are planning scenarios, not results, and names are left out.

What does Preston say about this on video?

The 100% Write-Off Playbook for 2025 (10 min, October 2025). Preston walks through 100% bonus depreciation, when Section 179 is the better tool, cost segregation on a purchased building, short-term rental participation, heavy vehicles, state conformity, and the QBI and estimated tax checks to run before December 31. Watch on YouTube.

The video was made in late 2025, so its year-end deadlines refer to 2025. The rules it covers for bonus depreciation, cost segregation, and Section 179 still apply in 2026.

Who does a cost segregation study?

A study is done by a specialist, not by your tax preparer. Most studies come from one of these:

• Cost segregation engineering firms. They visit or inspect the property and build the asset list.
• CPA firms with an engineering team. Some larger firms have engineers or construction cost estimators on staff.
• Remote or software studies. These use photos, plans, and cost data for smaller home-style rentals. They cost less and go into less detail.

Your CPA or enrolled agent reviews the study and puts the numbers on your return. When you compare providers, look for one that:

• Uses an engineer or construction cost estimator and explains the method.
• Visits the property, or reviews detailed photos, plans, and invoices.
• Gives you a line-by-line asset list, not one percentage.
• Supports the land value it uses.
• Will explain and defend the study if the IRS asks about it.

How do you get a cost segregation study done?

1. Check that you can use the loss. Decide which route applies: short-term rental, REPS, passive income, or business use.
2. Get two or three quotes from firms that use engineers and visit the property or review detailed records.
3. Give the firm the closing statement, the land value support, any appraisal, and invoices for work done before the property went into service.
4. Get the report before you file the return for the year the property was placed in service.
5. Your preparer reports it on Form 4562, with bonus depreciation on the 5, 7 and 15 year parts.
6. Keep the report with your tax file until at least three years after you sell.

Can you do cost segregation on a property you bought years ago?

Yes. This is called a lookback study. You do not amend old returns. Your preparer files Form 3115 for an automatic change in accounting method, and the depreciation you missed is taken in the current year as a Section 481(a) adjustment. Bonus depreciation on those older parts follows the rate for the year each part was placed in service, not the 2026 rate.

Here is how the look-back filing works:

1. Order the study. The engineer works out what each class should have been since the property went into service.
2. Your preparer figures the catch-up. It is the depreciation you could have claimed through last year, minus what you did claim. That is the Section 481(a) adjustment.
3. Form 3115 goes with your return. It is attached to the timely filed return for the year of the change, extensions included. A depreciation catch-up like this is usually an automatic change, designated change number 7 in Rev. Proc. 2025-23, with no IRS user fee.
4. A signed copy goes to the IRS in Ogden, Utah, no later than the day you file the return.
5. The catch-up is taken in one year. A negative adjustment, which lowers your income, is taken in full in the year of the change.

If you have filed only one return since the property went into service, you may not need Form 3115. Under IRS Publication 946, you adopt a depreciation method by using it on two or more returns in a row. Ask your preparer whether an amended return is the simpler fix.

A lookback also helps when you replace something. If a study shows the cost of an old roof or old carpet, you can write off what is left of that cost when you replace it, through a partial disposition election. Read more in the guides on Form 3115 for cost segregation and the 481(a) adjustment.

What mistakes make a study fail?

• A "rule of thumb" split. A spreadsheet that puts 30% in 5-year property with no asset list is the weakest kind of study under Publication 5653.
• Land valued too low. Every dollar moved from land to building needs support, such as the tax assessor ratio or an appraisal.
• Paying for a study you cannot use. A passive loss with no passive income is suspended.
• Ignoring the state return. Some states add bonus depreciation back.
• Forgetting the excess business loss cap. In 2026, business losses above $512,000 on a joint return carry forward under Section 461(l).
• Forgetting recapture. Selling soon turns the deduction back into ordinary income.

What happens when you sell?

The 5 and 7 year parts are Section 1245 property, and the depreciation on them comes back as ordinary income when you sell. The building share comes back as unrecaptured Section 1250 gain, taxed at up to 25%. Bonus depreciation on 15 year land improvements is also recaptured as ordinary income to the extent it beat straight-line depreciation.

Section 1245 recapture is limited to the gain on those parts, so it depends on what the used items are worth at the sale. A 1031 exchange defers recapture on the real estate. Some Section 1245 recapture can still come due in an exchange if the new property has less personal property than the old one, so check this with your CPA before you sign. The sample sale above shows the full math, and the depreciation recapture calculator runs it on your numbers.

That is why cost segregation is a timing tool. It pays best when you hold for many years, exchange through a 1031 exchange, or hold until death and your heirs get a stepped-up basis. See depreciation recapture on a short-term rental for the math.

What changed for 2026?

• 100% bonus depreciation is permanent for qualified property acquired after January 19, 2025 (Section 168(k), Notice 2026-11).
• The 2026 Section 179 limit is $2,560,000, with the phase-out starting at $4,090,000 of purchases (Rev. Proc. 2025-32).
• The 2026 excess business loss cap is $512,000 for joint filers.
• The recovery periods and the study standards did not change.

Related reading: how cost segregation lowers taxes, bonus depreciation on residential rentals, and the rental depreciation deduction guide. The tax strategy library lists every guide.

Which IRS sources back this up?

Read the rule itself before you rely on a summary, including this one.

• IRS Cost Segregation Audit Techniques Guide (Publication 5653)
• IRS Publication 946, How to Depreciate Property
• IRS Publication 527, Residential Rental Property
• IRS Notice 2026-11, interim guidance on 100% bonus depreciation
• Internal Revenue Code Section 168
• IRS Form 3115, Application for Change in Accounting Method
• Instructions for Form 3115, including the duplicate copy and the 481(a) period
• IRS Publication 544, Sales and Other Dispositions of Assets (recapture)
• IRS Form 4562, Depreciation and Amortization
• IRS Publication 925, Passive Activity and At-Risk Rules