The 1031 exchange is one of the most powerful tools in the tax code for real estate investors. It’s also one of the most misunderstood. Most investors know the headline: sell one property, buy another, defer the tax. But the mechanics underneath, the deadlines, the intermediary, the identification rules, the carryover basis, are what determine whether a 1031 actually works in practice. And they’re also what determine where cost segregation fits into the picture. Here’s how a 1031 actually works, and where cost seg can add value on both sides of the transaction.

What a 1031 Exchange Is

Section 1031 of the Internal Revenue Code lets you sell a property held for investment or business use and roll the proceeds into another like-kind property without recognizing capital gains or depreciation recapture in the year of sale. The gain isn’t forgiven. It’s deferred. Your basis in the new property carries over from the old one, so the tax liability moves with you into the replacement property. After the Tax Cuts and Jobs Act in 2017, §1031 only applies to real property. Personal property, equipment, vehicles, and similar assets, was taken out. That change matters for cost-segregated property, and I’ll come back to it. Many investors use 1031s repeatedly to trade up their portfolios and push the tax bill out indefinitely. If they hold until death, their heirs get a step-up in basis and the deferred tax goes away entirely.

The Timing Rules

Two deadlines run the show. You have 45 days from the sale of the relinquished property to identify potential replacement properties in writing. You have 180 days from that sale to close on one of them (or by your tax return due date for that year, whichever comes first). These are calendar days. They don’t pause for weekends or holidays. Within that 45-day identification window, you pick one of three identification methods:
  • 3-property
rule: identify up to three properties, no value limit.
  • 200%
rule: identify more than three, but their combined fair market value can’t exceed 200% of the relinquished property’s value.
  • 95%
rule: identify any number, but you have to actually acquire 95% of the total identified value. Miss the 45-day identification deadline or the 180-day closing deadline, and the exchange collapses into a taxable sale. There’s no extension or hardship exception.

The Qualified Intermediary

You can’t touch the proceeds. The moment you take actual or constructive receipt of the funds from the sale, the exchange is blown. That’s where the qualified intermediary (QI) comes in. The QI is a neutral third party who holds the proceeds between the two sales, handles the paperwork, and makes sure the safe harbor under Treasury Regulation §1.1031(k)-1 is satisfied. The QI has to be lined up before the sale closes. This is one of the most common reasons 1031s fail. Investors close the sale, then start looking for an intermediary, and by then it’s already too late.

What Qualifies as Like-Kind

Like-kind is broader for real estate than most people realize. A small multifamily can be exchanged for a shopping center. Raw land can be exchanged for an office building. Pretty much any real property held for investment or business use qualifies, as long as the replacement is also held for investment or business use. What doesn’t qualify: primary residences, property held for resale (like fix-and-flips or dealer inventory), and personal property of any kind. There’s also the question of boot. If you take cash out at closing, or your replacement property has less debt than the one you sold, that difference is taxable in the year of sale. Full deferral requires equal-or-greater value and equal-or-greater debt on the replacement property.

Cost Segregation Before the Sale

If you’re planning a 1031 and haven’t run a cost seg study on the property you’re selling, there’s still time to do one, and it can be worth it. A study before the sale lets you accelerate depreciation on short-life components in your final year of ownership. With 100% bonus depreciation now permanent for property placed in service after January 19, 2025 under the One Big Beautiful Bill Act, that final-year deduction can be substantial. The gain itself gets deferred through the 1031, so the accelerated depreciation doesn’t trigger immediate recapture. You’re capturing one more year of tax benefit before rolling the basis forward into the replacement property. One thing to flag: because §1031 after TCJA only applies to real property, the §1245 components identified in a cost seg study can create complications if the relinquished property’s §1245 mix doesn’t line up well with the replacement property’s. Worth modeling with your CPA before you list.

Cost Segregation After the Exchange

Once you close on the replacement property, you can run a cost seg study on it too. This is where the basis math matters. In a 1031, the replacement property’s depreciable basis splits into two parts:

  • Carryover
basis: the adjusted basis from the relinquished property, which continues its existing depreciation schedule.
  • Excess
basis: any additional investment above the relinquished property’s basis, typically from cash added or new debt. Cost seg on the excess basis works like a study on a regular acquisition. You identify short-life components, accelerate the depreciation, and potentially apply bonus depreciation. On the carryover basis, the treatment is more nuanced and depends on how the study is structured and how your CPA handles it on the return.

There are two practical takeaways here:

The bigger the step-up in value between the old and new property, the more excess basis you have to work with, and the more a cost seg study is worth running on the replacement. And the projected deductions need to be modeled correctly. Applying cost seg to the full purchase price of the replacement, as if it were a fresh acquisition, will overstate the benefit. The carryover basis has to be handled separately.

When a 1031 Isn’t the Right Tool

A 1031 isn’t the only way to manage the tax hit on a sale. Another approach is sometimes called the lazy 1031 or 1031 lite where you sell the property, recognize the gain, and then acquire a different property in the same tax year and use cost segregation to generate depreciation that offsets that gain. It works because gain from the sale of a passive rental is passive income under IRS §469. Depreciation from a new rental property is a passive loss. The two can offset each other without a formal exchange, a QI, or a 45-day clock.

The tradeoffs compared to a formal 1031:

  • You

get a full fresh basis on the new property, which means more depreciation going forward versus the constrained carryover basis in a 1031.

  • There’s

no 45-day or 180-day deadline. You can buy when the right deal actually shows up.

  • But

the sale itself is still a taxable event. You need enough passive loss in the same year to absorb the gain. This approach tends to work well for investors rotating into syndications, making partial portfolio exits, or situations where the gain is modest enough that the friction of a formal 1031 isn’t worth it.

Making the Call

The 1031 is a strong tool when you want full deferral of a sizable gain, you’re staying in direct real estate, and you have a clear replacement property in mind. The same-year offset is a better fit when flexibility and timing matter more. Either way, cost segregation has a role to play. Before the sale, after the exchange, or on a new acquisition that offsets the gain. The common thread is timing the deduction to the year you actually need it. If you’re planning a sale in the next 12 months, it’s worth modeling both paths before you commit. Get a free quote with Maven Cost Segregation.