Cost Segregation Calculator: What a Study Really Buys You

Introduction

Cost segregation is usually sold as a tax saving. It is a tax deferral, and the difference matters — because the deductions a study pulls into year one are deductions you do not get in years six through twenty-eight.

TL;DR: A study does not create depreciation. It reallocates it. On the defaults, year one goes from $11,636 to $56,727 of deduction — worth $14,429 at a 32% marginal rate. Years two through five stay above straight-line while the short-life property depreciates, and from year six onward the study column drops to $8,727 against straight-line's $11,636 and stays there. By the end of the recovery period both columns total the same building basis.

The formula

Only the building depreciates — land never does:

Total basis    = purchase price
                 + improvements

Building basis = total basis
                 − land value

Straight-line  = building basis
                 ÷ recovery period

recovery period: 27.5 yr residential
                 39 yr commercial

A cost segregation study reclassifies part of the building into shorter-life categories — 5, 7 and 15-year property such as appliances, carpet, cabinetry, landscaping and site work — which are eligible for bonus depreciation:

Reclassified   = building basis
                 × reclassified %

Bonus year one = reclassified basis
                 × bonus %

Year-one total = bonus
                 + (long-life basis
                    ÷ recovery period)

Worked example

The defaults: a $400,000 residential rental, 20% land, 27.5-year recovery. A study reclassifies 25% of building basis, and bonus depreciation is at 60%. Marginal rate 32%.

• Land: $400,000 × 20% = $80,000 — never depreciable
• Building basis: $320,000
• Straight-line: $320,000 ÷ 27.5 = $11,636 a year

With a study:

• Reclassified to short life: $320,000 × 25% = $80,000
• Taken as bonus in year one: $80,000 × 60% = $48,000
• Remaining long-life basis: $240,000 ÷ 27.5 = $8,727
• Year-one deduction: $48,000 + $8,727 = $56,727
• Advantage over straight-line: $45,091
• Tax deferred in year one at 32%: $14,429

Where the columns cross

This is the part the sales pitch omits, and it is why the schedule is on the page.

Year	Straight-line	With study
1	$11,636	$56,727
2–5	$11,636	$15,127
6–28	$11,636	$8,727

Years two through five are still ahead, because the $32,000 of reclassified basis not taken as bonus depreciates over five years. But from year six the short-life property is fully written off, and the study column drops to $8,727 — permanently below straight-line, for twenty-three years.

Both columns total $320,000. That is the whole point: the building basis is fixed, and a study only changes when you claim it.

So the real value of a study is the time value of money on the deferral, plus the option value of having deductions in a year when you can actually use them. Both are genuine. Neither is "saving $14,429 in tax."

Depreciation recapture is the bill at the end

When you sell, depreciation claimed is recaptured as unrecaptured Section 1250 gain, taxed federally at up to 25% — a higher rate than long-term capital gain. Accelerating depreciation therefore accelerates your recapture exposure too.

Two things blunt this, and they are the reason studies are still worth doing:

A 1031 exchange defers the recapture along with the gain. If you intend to exchange rather than sell, the recapture may be deferred indefinitely.

Short-life property recaptures differently. Personal property reclassified by a study is subject to Section 1245 recapture at ordinary rates rather than the 25% 1250 rate — which can be worse, not better, depending on your bracket. This is genuinely complicated and it is a question for your CPA, not a calculator.

Whether a study is worth it

Studies cost roughly $4,000 to $15,000 for a residential rental depending on scope and whether it is a full engineering study or a modelled one. Against $14,429 of year-one deferral on the example, the arithmetic is tight rather than obvious.

It tends to be worth it when:

• The property is large enough that the reclassified basis is meaningful — the benefit scales with basis and the cost does not
• You have income the deduction can actually offset this year
• You intend to hold long-term or exchange, so recapture is deferred rather than imminent
• You are in a high marginal bracket, since the deferral is worth your rate

It tends not to be worth it when:

• The property is small and the fee eats the benefit
• Passive activity loss rules mean the deduction is suspended anyway — which is the single most common reason a study disappoints
• You plan to sell within a few years, so recapture arrives before the deferral has earned anything

The passive loss trap

This is the one that catches people. Rental losses are generally passive, and passive losses can only offset passive income unless you qualify as a real estate professional or fall under the $25,000 active-participation allowance, which phases out entirely by $150,000 of adjusted gross income.

So a high-earning W-2 investor may generate a $45,091 deduction that cannot be used this year at all. It carries forward, which is not worthless — but the whole case for paying for a study is having the deduction now, and carrying it forward for a decade is not that.

Short-term rentals are a notable exception: an STR with average stays of seven days or less is not automatically a rental activity under the passive loss rules, which is why STRs and cost segregation come up together so often. See the short-term rental calculator.

Where this calculator is deliberately simple

The reclassified basis not taken as bonus is spread evenly over five years, rather than through the actual 5, 7 and 15-year MACRS tables. That would need three more schedules for a second-order effect on the shape of years two to five.

No mid-quarter or partial-year convention. Real first-year depreciation depends on the month you placed the property in service. The monthly straight-line figure is provided so you can prorate.

Bonus depreciation is an input, not a constant. It is set by statute and has changed repeatedly. Check the rate for your placed-in-service year rather than trusting any default, including this one.

No recapture modelling, no state variation, no AMT. All real, all beyond what a single-page calculator can honestly do.

This is not tax advice. Cost segregation genuinely requires a professional — both the study itself and the decision to commission one.

FAQ

What is cost segregation?

An engineering-based analysis that reclassifies parts of a building into shorter depreciation lives — appliances, flooring, cabinetry, landscaping, site work — so those components can be depreciated over 5, 7 or 15 years instead of 27.5 or 39, and may qualify for bonus depreciation.

Is cost segregation a tax saving or a deferral?

A deferral. The total depreciation over the property's life is identical either way; a study changes only the timing. Its value is the time value of money on the deferred tax, plus the ability to place deductions in years you can use them.

How much does a cost segregation study cost?

Roughly $4,000 to $15,000 for a residential rental, more for commercial or complex properties. Modelled or "DIY" studies cost less and carry more audit risk. Compare the fee against the year-one deferral at your marginal rate, then against whether you can actually use the deduction.

What percentage of a building can be reclassified?

Typically 20–35% of building basis on residential rental, and often more on properties with extensive site work, landscaping or specialised fixtures. The default here is 25%. A study will give you the real figure; anyone quoting you a number before inspecting the property is guessing.

Can I do a cost segregation study on a property I already own?

Yes. You can apply it to a prior-year acquisition and claim the accumulated missed depreciation in the current year through a change in accounting method — Form 3115 — without amending returns. That "catch-up" deduction is often larger than a fresh study's year-one benefit, which makes previously-held properties good candidates.

Does bonus depreciation still apply?

The bonus percentage is set by statute and has been changed several times. Rather than trusting any published figure, including the default in this calculator, confirm the rate applicable to your placed-in-service year with your CPA.

Conclusion

Compute the year-one deferral, then ask the two questions the calculator cannot: can you use the deduction this year, and do you intend to exchange rather than sell? If the answers are yes and yes, a study is usually worth its fee. If either is no, look hard at the schedule above and the twenty-three years where the study column sits below the straight-line one.