Cost segregation calculator: test a first-year scenario
This calculator is for a new acquisition with components independently confirmed as eligible for 100% federal bonus depreciation. It does not determine eligibility or calculate a prior-year Form 3115 adjustment. Enter your own assumptions; property type does not establish a reclassification percentage or a recovery period.
Calculation method and a worked example
Depreciable basis equals acquisition basis less land. The assumed reclassified portion receives 100% bonus; the remaining building uses straight-line GDS depreciation with a mid-month fraction of (12.5 minus the calendar month number) divided by 12. The same fraction applies to the without-study comparison. The difference is multiplied by the entered usable percentage and federal marginal rate, then the entered fee is subtracted.
For $1,000,000 of basis, 20% land, 20% qualifying reclassification, 27.5 years and January service, the additional first-year deduction is approximately $154,424. If all of it is usable at an assumed 32% rate, the illustrative federal reduction is $49,416; after a $3,000 entered fee, the current cash benefit is $46,416. If none is currently usable, the immediate reduction is $0 and the fee still costs $3,000.
This is a sensitivity calculation, not a tax-return estimate. It excludes state tax, deduction interactions, the tax treatment of the fee, future depreciation differences, sale recapture, financing and time value. A full holding-period projection may change the decision. See IRS Publication 946 and Publication 925 for the underlying depreciation and loss-limitation rules.
Related-party acquisition review · Bonus elections by asset class · Request a property-specific study proposal
How Accurate Is a Cost Segregation Calculator Before You Pay for a Study?
A calculator can produce a useful feasibility range, but it cannot produce the depreciation schedule you file. Its accuracy depends on whether it starts with the property's actual depreciable basis, removes land, separates assets already priced on the closing statement, reflects the building's real use and components, applies the law for the correct acquisition and placed-in-service dates, and tests whether the resulting loss is usable. A flat percentage of purchase price is not a defensible cost segregation study.
Use a calculator to answer a decision question: is the likely timing benefit large enough to justify a property-specific study and tax review? Do not use it to claim that a certain percentage of the building automatically qualifies, that every short-life asset receives bonus depreciation, or that a projected deduction equals cash tax saved.
What the Estimate Can and Cannot Tell You
| Calculator can screen | Calculator cannot prove |
|---|---|
| A reasonable low-to-high short-life allocation based on the property type and known features | The classification and cost of each actual component |
| Illustrative first-year and multi-year federal depreciation | The final Form 4562 or fixed-asset schedule |
| Whether projected timing benefits appear to exceed the study fee | Whether passive-loss, basis, at-risk, or excess-business-loss limits allow a current deduction |
| Sensitivity to land value, bonus rate, tax rate, improvements, and hold period | State conformity, recapture on sale, accounting-method procedure, or audit support for the specific property |
The Inputs That Control Calculator Accuracy
- Tax basis, not just purchase price. Start with the property's tax basis under the acquisition facts. Closing costs, separately stated personal property, credits, assumed liabilities, and later capital improvements can change the number.
- A supportable land allocation. Land is not depreciable. County assessments, appraisals, purchase documents, and local market evidence may support an allocation; a universal 15% assumption does not.
- Placed-in-service dates. Acquisition date and placed-in-service date are different. Depreciation begins when the property is ready and available for its intended income-producing use, and separate improvements may have separate service dates.
- Property use and component profile. A furnished rental, medical office, warehouse, restaurant, self-storage facility, and apartment building do not have interchangeable asset mixes.
- Improvement detail. Renovation invoices may already identify furniture, equipment, land improvements, building systems, repairs, and structural work. Applying one percentage to all improvement spending can double count or misclassify costs.
- Bonus-depreciation eligibility. Current law generally restored 100% bonus depreciation for qualifying property acquired after January 19, 2025, subject to the statutory requirements and transition rules. A prior-year property uses the rules, elections, and service date for that year.
- Usable-loss analysis. Tax savings depend on the taxpayer's marginal rate and ability to use the deduction after passive-activity, material-participation, basis, at-risk, and excess-business-loss limits.
- Expected sale date and state rules. Accelerating deductions may increase later recapture, and many states do not follow federal bonus depreciation. A federal-only model can overstate near-term cash benefit.
Do Not Determine 27.5-Year or 39-Year Property From Average Guest Stay Alone
The seven-day and 30-day average-stay tests are important to the passive-activity regulations, but they do not by themselves decide the building's MACRS recovery period. Residential rental property generally turns on whether the building or structure meets the statutory dwelling-unit and rental-income test; nonresidential real property is the residual category. An Airbnb is not automatically 39-year property merely because the average stay is seven days or less.
This distinction changes the calculator's straight-line baseline. It does not eliminate cost segregation, but it can materially change the incremental deduction shown. Confirm the property's use, income mix, and placed-in-service facts before comparing the estimate with 27.5-year or 39-year depreciation.
Worked Estimate: Use a Range, Not a Flat Percentage
Assume an investor purchases a rental property for $900,000. A supportable allocation assigns $180,000 to land, leaving $720,000 of depreciable basis before separately stated personal property and later improvements. The property is acquired and placed in service after January 19, 2025, and the owner has not elected out of bonus depreciation.
A preliminary review suggests that 20% to 30% of depreciable basis could fall into shorter-life classes. That produces a screening range of $144,000 to $216,000, not a promised result:
| Calculation | Low case | High case |
|---|---|---|
| Purchase price | $900,000 | $900,000 |
| Less land | ($180,000) | ($180,000) |
| Depreciable basis screened | $720,000 | $720,000 |
| Illustrative short-life allocation | 20% | 30% |
| Projected short-life basis | $144,000 | $216,000 |
| Remaining building basis | $576,000 | $504,000 |
If every projected short-life component is bonus-eligible and the taxpayer has not elected out, current federal law may allow an immediate deduction for that qualifying basis, plus the applicable first-year depreciation on the remaining building. But the incremental benefit is the cost-segregated result minus the depreciation the taxpayer would have claimed without the study. The amount actually reducing current tax can be smaller when losses are passive or otherwise limited.
Run at least four sensitivities before approving a study: land allocation, short-life percentage, deduction usability, and sale timing. If the study fee only works in the most aggressive case, the decision is not ready.
Decision Example: A Large Deduction That Is Not Currently Usable
Suppose the same study projects $180,000 of additional first-year depreciation, and the owner is in a 32% federal bracket. Multiplying $180,000 by 32% suggests $57,600 of federal tax value. That is not automatically current-year cash savings.
If the property is a passive activity and the owner has no passive income, the loss may be suspended. The deduction can still have value in a later year, but the study decision should compare the present value of that deferred benefit with the fee, expected holding period, state treatment, and recapture exposure. A calculator that labels $57,600 as an immediate refund without testing loss usability is overstating the result.
How 100% Bonus Depreciation Changes the Estimate
Current federal law generally restored 100% bonus depreciation for qualifying property acquired after January 19, 2025, subject to the statutory requirements and transition rules. Cost segregation can identify 5-year, 7-year, and 15-year property that may qualify, but the building shell and other long-lived real property do not become bonus-eligible.
Do not apply the current bonus rate to every lookback property. A property placed in service in an earlier year requires a year-specific analysis of acquisition timing, binding-contract rules, service date, elections, asset eligibility, and depreciation already claimed. The calculator should expose the bonus-rate assumption instead of hiding it.
How Improvements Enter the Model
Capital improvements can increase depreciable basis, but each project must be analyzed rather than added to one percentage bucket. Preserve invoices, contracts, drawings, and service dates so the estimate can separate:
- stand-alone furniture, equipment, appliances, and other personal property;
- land improvements such as qualifying paving, fencing, landscaping, or site lighting;
- building components that remain 27.5-year or 39-year property;
- repairs that may be currently deductible under the tangible-property regulations;
- replaced components that may support a partial-disposition analysis; and
- assets already priced separately at acquisition, which should not be counted twice.
HVAC, electrical, plumbing, roofs, gutters, and similar systems are not automatically short-life property. Classification depends on what the component serves, how it relates to the building, and the controlling authorities. A calculator that labels every renovation dollar as 5-year or 15-year property is not reliable.
How to Calculate a Defensible Feasibility Range
- Establish depreciable basis. Reconcile the closing statement, land allocation, separately stated assets, capitalized acquisition costs, credits, and post-acquisition improvements.
- Choose a property-specific allocation range. Use a low and high short-life percentage based on the actual asset profile, not a universal percentage of purchase price.
- Apply year-specific depreciation law. Model the proper recovery periods, conventions, bonus percentage, elections, and service dates for each asset class.
- Calculate the incremental deduction. Subtract the depreciation that would be allowed without cost segregation from the cost-segregated schedule.
- Test federal usability. Apply passive-loss, material-participation, basis, at-risk, and excess-business-loss rules before calling the deduction a current tax benefit.
- Model state treatment separately. Many states require a bonus-depreciation addback or a different recovery schedule.
- Compare the net present value. Include the study fee, tax-return implementation, state work, expected hold period, later recapture, and the timing of any suspended loss.
Catch-Up Depreciation for a Prior-Year Property
A calculator can screen a lookback opportunity, but it cannot calculate the final Section 481(a) adjustment from purchase price alone. The adjustment compares depreciation actually claimed through the beginning of the change year with depreciation allowable under the corrected method. That requires the original and current fixed-asset schedules, basis support, service dates, prior elections, dispositions, improvements, and the applicable Form 3115 procedure.
A qualifying automatic accounting-method change can often correct an impermissible depreciation method without amending every open year, but the exact procedure depends on the facts and current revenue procedure. A study completed for an older property also uses the bonus rules from the original placed-in-service year; it does not simply apply today's rate.
When a Professional Study Adds Value
The IRS Cost Segregation Audit Techniques Guide explains that a quality study identifies the preparer and methodology, reconciles total project costs, explains land and building allocations, classifies assets with legal support, and documents how costs were determined. When actual component costs are unavailable, cost-estimating techniques may be needed.
A calculator does none of that component-level work. A professional study is most useful when the estimated benefit is material, the property has a complex mix of assets or improvements, records are incomplete, the property was placed in service in a prior year, or the taxpayer needs implementation support for Form 4562, Form 3115, state depreciation, and future dispositions.
Documents to Gather Before Relying on an Estimate
- Purchase agreement, closing statement, appraisal, and land-allocation support.
- Placed-in-service date and evidence the property was ready and available for rent.
- Current federal and state depreciation schedules and prior Form 4562 filings.
- Improvement invoices, construction draws, contracts, plans, photos, and separate service dates.
- Furniture, equipment, and other personal-property schedules.
- Rental-use history, average guest stay, services provided, and material-participation records when relevant.
- Expected hold period, planned sale or exchange, tax rates, passive income, suspended losses, basis, and at-risk information.
Common Calculator Failure Points
- Applying a percentage to total purchase price: land and separately stated assets must be handled first.
- Treating every STR as 39-year property: average stay affects passive-activity analysis but does not alone decide the building recovery period.
- Using one allocation for every property type: component profiles differ materially.
- Applying today's bonus rate to an older property: lookback calculations are year-specific.
- Calling a deduction “tax savings” before testing usability: suspended losses do not create immediate cash savings.
- Ignoring state nonconformity: a federal deduction may require a state addback and separate schedule.
- Ignoring the exit: accelerated depreciation can change later recapture and after-tax sale economics.
- Filing from the estimate: a percentage model does not establish actual asset classifications or costs.
Primary Sources and Review Standard
- IRS Cost Segregation Audit Techniques Guide
- IRS Publication 946, How To Depreciate Property
- Instructions for Form 4562
Reviewed September 24, 2026. Calculator outputs are planning estimates, not tax-return positions. Confirm current federal and state law for the property's dates and the taxpayer's facts.
Use AE's interactive cost segregation estimator for an initial range, then review the inputs and loss usability before paying for a study.