Is cost segregation worth it? The break-even math

The break-even formula

The whole question reduces to one comparison: the modeled tax benefit in your first year versus what the study costs. Everything else feeds those two numbers. The benefit side has three inputs that multiply together.

First, the reclassified basis — the slice of your depreciable basis (the building, not the land) that an engineering-style study moves out of the 27.5- or 39-year schedule and into shorter 5-, 7-, and 15-year lives. For a residential rental this share is commonly in the 20–35% range, though it varies with property type and finishes; treat any percentage as an estimate until a study measures your specific asset. Second, the bonus depreciation rate for the year the property was placed in service — the portion of those short-life components you can write off immediately. Third, your marginal tax rate — federal plus, where it applies, state.

So the rough first-year benefit is: reclassified basis × bonus rate × marginal rate. Compare that modeled figure to the study cost. When the benefit is several times the cost, the decision is easy. When it is a near tie, the answer is genuinely “it depends.”

A worked example: a $400,000 long-term rental

Suppose you bought a single-family rental and, after carving out land, your depreciable building basis is $400,000. Assume an estimated 28% of that basis reclassifies into short-life property, the property was placed in service in a 100% bonus year, and your combined marginal rate is 32%. The modeled first-year picture looks like this:

• Depreciable building basis: $400,000
• Estimated reclassified to 5/7/15-year life (28%): $112,000
• Eligible for 100% bonus in the placed-in-service year: $112,000
• Modeled first-year deduction acceleration vs. straight-line: roughly $100,000 after netting out the depreciation you would have taken anyway
• Modeled first-year tax impact at 32%: about $32,000

Set a roughly $32,000 modeled benefit against a study cost in the low thousands and the ratio speaks for itself. These figures are modeled, not promised: the actual first-year number depends on the §481(a) catch-up if you are doing this on a property you have already owned, the bonus rate fixed by your placed-in-service year, state conformity (several states decouple from federal bonus), the §469 passive-activity rules covered below, and your entity structure. We model the estimate; your tax preparer files the return.

When it clearly pays

The math is lopsided in your favor when the inputs stack up. Look for these together:

• Higher building basis. A larger reclassifiable pool means a larger benefit against a study cost that does not scale with property size.
• A 100% bonus placed-in-service year. Bonus has phased over time; full expensing pulls the most benefit into year one. Partial-bonus years still work — the benefit is simply spread out more.
• Losses you can actually use. Acceleration only helps if the resulting loss offsets income. Active participation, real-estate-professional status (REPS), or material participation in a short-term rental can make those losses usable in the current year rather than suspended. Our companion guide on passive loss rules walks through who qualifies.
• A 32% or higher marginal bracket. Every dollar of deduction is worth your marginal rate. At 32%, 35%, or 37%, the same reclassification is worth far more than it is at the bottom of the schedule.

You do not need all four; the more that line up, the wider the margin over the study cost.

When it is genuinely marginal

Honesty cuts both ways. In some situations the numbers are thin, and it is better to know that going in. The math — not the seller — decides.

• Low basis. On a small-basis property the reclassified pool may be modest, and a fixed study cost eats a larger share of the benefit.
• A low bracket. In the 10–12% range each deduction dollar simply returns less, so the same reclassification produces a smaller modeled benefit.
• Trapped passive losses. If you cannot meet active participation or REPS and have no passive income to absorb the loss, the deduction is real but suspended — it carries forward rather than helping this year. The benefit is deferred, which weakens the present-value case.
• A near-term sale. If you plan to sell within a year or two, recapture (next section) can claw back much of the timing benefit before it has a chance to compound.

None of these means “never” — a marginal case can still pencil out, and circumstances change. It means the spread between benefit and cost is narrow enough that you should run the numbers carefully rather than assume.

Recapture: the part most pages skip

Cost segregation accelerates deductions; it does not create extra ones. When you sell, the IRS “recaptures” depreciation you took. Under §1245, the personal-property and land-improvement components a study reclassifies are recaptured as ordinary income to the extent of depreciation claimed. Under §1250, the real-property portion is subject to unrecaptured gain taxed at a capped rate. In plain terms: you pulled deductions forward, and some of that benefit is settled up at sale.

This is why cost segregation is best understood as a timing trade, not free money. The value is in the time between deducting early and paying later — the use of those dollars in the interim, and the chance that you are in a different position when the bill comes due. A few factors change the calculus materially:

• A long hold. The longer you own, the more years the accelerated deduction works for you before any recapture — and the stronger the present-value case.
• A 1031 exchange. A properly structured like-kind exchange can defer the gain (and the recapture with it) into the replacement property, pushing the settle-up further out.
• Your rate then vs. now. Recapture lands at the rates in effect when you sell, against the marginal rate you saved at today. That spread can help or hurt.

For background on the depreciation mechanics and recapture, the authoritative references are IRS Publication 946 (How to Depreciate Property) and the IRS Cost Segregation Audit Techniques Guide (Publication 5653).

Run your own numbers

The formula above is general; your answer is specific. Whether the spread is wide or thin comes down to your basis, your placed-in-service year, your bracket, and whether your losses are usable — which is exactly what the qualifier on our homepage asks. Six questions, an honest verdict, and an estimated range, in about thirty seconds. If you bought years ago and never accelerated, the lookback path (a §481(a) catch-up via Form 3115) is covered at catchupdepreciation.com, and our guide on qualifying after years of ownership explains the timing. When the math is clearly in your favor and you are ready, you can order a study.