Key Takeaways
- The 45-day identification clock starts on the day of closing, not the day you receive proceeds. One day off disqualifies the entire exchange.
- Investors who miscount the 180-day window forfeit deferred gains. On a $900,000 relinquished property with a $200,000 basis, that error costs roughly $140,000 in federal tax at the 20% long-term rate plus the 3.8% NIIT.
- Identify up to three replacement properties by value or use the 200% rule to identify more. Acquire at least one within 180 days of closing to preserve the deferral.
- Tool: Run your 1031 exchange numbers with the CalcMoney calculator →
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What a 1031 Exchange Actually Defers
A 1031 exchange does not eliminate capital gains tax. It defers it. The IRS allows investors to roll proceeds from one investment property into a like-kind replacement property without recognizing the gain at the time of sale. The deferred gain carries into the new property's cost basis.
That distinction matters. Investors who treat a 1031 as a permanent tax elimination often face a compounded bill years later when they finally sell without exchanging. Understanding exactly what you are deferring, and for how long, shapes every decision from deal structure to exit planning.
The two numbers that determine whether your exchange qualifies: 45 days and 180 days. Both are calendar-day counts with no extensions except in presidentially declared disasters.
The 45-Day Identification Window: How to Calculate It Correctly
The IRS requires you to identify potential replacement properties in writing within 45 calendar days of closing on the relinquished property.
The count begins on the day after closing. If you close on June 1, day one is June 2. Day 45 is July 16. That written identification must be delivered to a qualified intermediary, the seller of the replacement property, or another party to the exchange before midnight on day 45.
No exceptions apply for weekends or holidays. If day 45 falls on a Sunday, your identification deadline is still that Sunday.
The Three-Property Rule
You may identify up to three properties regardless of their combined value. This is the most commonly used rule.
Example: You sell a rental property in Austin for $750,000. You identify a duplex in Phoenix ($420,000), a small office building in Denver ($680,000), and a warehouse in Dallas ($1,100,000). All three qualify under the three-property rule. You must close on at least one before day 180.
The 200% Rule
If you want to identify more than three properties, their combined fair market value cannot exceed 200% of the relinquished property's sale price.
Example: You sell for $750,000. Under the 200% rule, your identified replacements cannot exceed $1,500,000 in total. You could identify five properties worth $280,000, $310,000, $240,000, $390,000, and $275,000. Their combined value is $1,495,000. That clears the threshold by $5,000.
The 95% Rule
A third option exists for investors who identify properties exceeding 200% of the sale price. You must acquire at least 95% of the total identified value. This rule is rarely practical because it requires near-complete acquisition of everything identified.
The 180-Day Closing Window: When the Clock Really Ends
You have 180 calendar days from the closing of the relinquished property to close on your replacement. This deadline runs concurrently with the 45-day window. It does not restart after identification.
One critical overlap: if your tax return for the year of the relinquished sale is due before day 180, you must close by the earlier of the two dates. File an extension to preserve the full 180-day window.
Example: You close on the relinquished property on November 15, 2025. Day 180 falls on May 14, 2026. Your 2025 federal return is due April 15, 2026. Without an extension, your effective closing deadline is April 15, not May 14. Filing Form 4868 preserves the remaining 29 days.
Worked Example 1: Calculating Deferred Tax on a Standard Exchange
An investor purchased a fourplex in 2015 for $320,000. Accumulated depreciation over ten years totals $94,545 (residential rental property depreciates over 27.5 years: $320,000 divided by 27.5 equals $11,636 per year; multiplied by 8.12 full years equals $94,545).
The investor sells the fourplex in 2026 for $875,000.
Adjusted basis: $320,000 minus $94,545 equals $225,455.
Total gain: $875,000 minus $225,455 equals $649,545.
Depreciation recapture: $94,545 taxed at 25% equals $23,636.
Remaining capital gain: $649,545 minus $94,545 equals $555,000, taxed at 20% for this income level equals $111,000.
Net Investment Income Tax (3.8%): $649,545 multiplied by 0.038 equals $24,683.
Total tax without exchange: $23,636 plus $111,000 plus $24,683 equals $159,319.
A completed 1031 exchange defers the full $159,319. That capital stays invested in the replacement property, compounding rather than flowing to the Treasury.
Worked Example 2: Partial Exchange and Boot Calculation
Not every exchange is clean. When the replacement property costs less than the relinquished property, the difference is taxable "boot."
An investor sells a commercial lot for $1,200,000 with an adjusted basis of $400,000. The gain is $800,000. The investor identifies and closes on a replacement property for $1,050,000.
Boot: $1,200,000 minus $1,050,000 equals $150,000.
The $150,000 in boot is taxable in the year of the exchange. The remaining $650,000 in gain defers into the new property's basis.
Tax on boot: At a 20% long-term rate plus 3.8% NIIT, the effective rate is 23.8%. $150,000 multiplied by 0.238 equals $35,700 owed in the exchange year.
Deferred tax: $650,000 multiplied by 0.238 equals $154,700, deferred until eventual disposition.
The lesson: matching or exceeding the sale price of the relinquished property is not optional if you want full deferral. Every dollar of equity reduction creates a taxable event.
Like-Kind Requirements: What Qualifies and What Does Not
The IRS definition of "like-kind" for real property is broader than most investors assume. Any real property held for investment or business use qualifies for exchange into any other real property held for investment or business use.
Qualifying exchanges include: residential rental into commercial, raw land into industrial, one state to another. The properties do not need to be in the same asset class.
What disqualifies a property: personal residences, property held primarily for resale (dealer property), foreign property exchanged for domestic property, and any property not held for productive use in a trade, business, or investment.
A vacation home requires careful structuring. The IRS safe harbor requires the property to be rented at fair market value for at least 14 days per year and limited personal use to the greater of 14 days or 10% of the days it was rented at fair market value.
Qualified Intermediary: The Structural Requirement
You cannot touch the proceeds. If sale proceeds pass through your hands for even one day, the exchange fails regardless of intent.
A qualified intermediary (QI) holds the funds between the sale of the relinquished property and the purchase of the replacement. The QI must be in place before closing on the relinquished property. Retroactive arrangements do not qualify.
QI fees typically range from $800 to $1,500 for a straightforward forward exchange. Reverse exchanges, where you acquire the replacement property before selling the relinquished property, cost $3,500 to $7,000 or more. Reverse exchanges add a separate 180-day window for the relinquished property sale but carry their own structural complexity.
Basis Calculation in the Replacement Property
The deferred gain does not disappear. It reduces the cost basis of the replacement property.
Continuing Worked Example 1: The investor purchases a replacement fourplex for $950,000. The adjusted basis carried over from the relinquished property is $225,455. The new depreciable basis is $225,455 plus $75,000 (the additional cash invested) plus any closing costs added to basis.
This lower basis means higher future depreciation recapture and a larger capital gain on the eventual sale. A chain of exchanges can defer gains indefinitely. Death resets basis to fair market value under current law (the step-up provision), eliminating deferred gains entirely for heirs.
Run Your Own Numbers Before You Close
The 45-day and 180-day deadlines are fixed. The tax math, however, depends entirely on your adjusted basis, depreciation schedule, and replacement property price. Small errors in those inputs produce large errors in your liability estimate.
The CalcMoney 1031 exchange calculator lets you input your sale price, original purchase price, years held, and accumulated depreciation to produce a precise deferred tax figure and boot calculation. Run the numbers before you identify properties, not after. The identification deadline is non-negotiable once the clock starts.
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