Section 121 excludes up to $250K of gain ($500K for married couples) on a primary residence, tax-free and with no reinvestment required. Section 1031 defers unlimited gains on investment property but requires reinvesting in real estate. Different properties, different rules - and on a property that has been both, you can sometimes use both.
Sell a property that has climbed in value and the tax code offers two very different doors. One lets you exclude a slice of the gain and walk away with cash. The other lets you postpone the tax on the entire gain, as long as you put the money back into real estate. They apply to different kinds of property and follow different rules, and once in a while they meet on the same house.
How each provision works
Section 121, the primary residence exclusion. It lets you exclude up to $250,000 of gain from your income, or $500,000 if you're married filing jointly. To qualify, you must have owned and lived in the home as your primary residence for at least two of the past five years, and you can claim the exclusion once every two years. There's no reinvestment requirement, so you can take the cash, and the excluded tax is gone for good rather than postponed.
Section 1031, the like-kind exchange. It defers capital gains tax, with no dollar cap, on real property held for investment or business use. The condition is reinvestment: you have to roll the proceeds into like-kind real property - broadly, other real estate held for investment - within strict deadlines. You can do it as many times as you like. The tax is deferred rather than erased, though estate planning can make that permanent: heirs inherit at a stepped-up basis, meaning the cost basis resets to the property's value at death and the deferred gain is wiped out for income-tax purposes. A 1031 also requires a qualified intermediary - a third party who holds the sale proceeds so they never pass through your hands - plus extensive documentation.
Key differences
Factor | Section 121 | Section 1031 |
|---|---|---|
Property type | Primary residence | Investment/business property |
Max benefit | $250K/$500K exclusion | Unlimited deferral |
Reinvestment required | No | Yes (like-kind real property) |
Holding requirement | 2 of past 5 years as primary residence | Held for investment (no minimum specified) |
Frequency | Once every 2 years | Unlimited |
Tax treatment | Permanent exclusion | Deferral (potentially permanent via stepped-up basis) |
Depreciation recapture | Generally not applicable (personal residence isn't depreciated) | Deferred entirely |
Complexity | Low (claim on tax return) | High (QI, deadlines, documentation) |
Using both on the same property
When a property has served as both your home and a rental, both provisions can sometimes apply to the same sale. Two situations come up most often.
Scenario 1: Lived in it, then rented it. Say you live in a house for eight years, then rent it out for three. Two of the past five years were still owner-occupied, so you meet Section 121's two-of-five use test - but you're near the edge, since those residence years keep sliding toward the back of the window as the rental period grows. While you're inside the window, you can potentially exclude gain up to the 121 limit and defer the remainder through a 1031 exchange.
The gain has to be split between "qualified use," the stretch when the house was your residence, and "non-qualified use," the rental or vacant periods. The part tied to non-qualified use doesn't get the 121 exclusion, but it may be deferred under 1031.
Scenario 2: Rented it, then lived in it. Say you rent a property for five years, move in, and live there for three. You can potentially exclude up to $250K/$500K under Section 121. But rules that took effect after 2008 require the gain to be allocated, and the five rental years count as non-qualified use that shrinks the exclusion.
Important limitations. The American Jobs Creation Act of 2004 added restrictions on using Section 121 for a property acquired through a 1031 exchange. A home you obtained in a like-kind exchange must be owned for at least five years before the Section 121 exclusion can apply, and mixed-use allocations between qualified and non-qualified use are nuanced. Gain attributed to rental periods may not be excludable. All of this makes the combined strategy more complicated than it first appears, so consult your CPA before relying on both provisions.
Converting investment to personal (or vice versa)
Investment to personal. You can 1031 exchange into a property, hold it as a rental for the required period, then convert it to your primary residence. Once you've met the five-year ownership requirement and the two-of-five use test, a portion of future gain may qualify for Section 121.
Personal to investment. You move out of your primary home, convert it to a rental, hold it as investment property for a reasonable period - two or more years is a commonly cited benchmark - and then 1031 exchange it. You forfeit the Section 121 exclusion on that sale but defer the full gain through 1031. This route is aimed at gains that run past the 121 limits.
Example. Suppose your home has appreciated $800,000. The 121 exclusion covers $500,000 for a married couple filing jointly, which leaves $300,000 of taxable gain. Convert the home to a rental and 1031 exchange it instead, and you can defer the full $800,000. Whether that comes out ahead depends on your timeline, the conversion period required, and your estate planning goals.
Where each provision fits
Section 121 is the provision in play when:
- The gain is under $250K/$500K
- You want the cash with no reinvestment obligation
- You want a permanent exclusion rather than deferral
- The property has been your primary residence for at least two of the past five years
Section 1031 is the provision in play when:
- The gain exceeds the 121 limits
- The property is investment or business use
- You want to keep building a real estate portfolio
- Estate planning through a stepped-up basis is part of your strategy
Both can apply when:
- A property has mixed use, with both primary residence and rental history
- The gain significantly exceeds the 121 limit and you're willing to convert and hold
Section 121 is the simpler tool: a permanent exclusion, but only on a primary residence and capped at $250K/$500K. Section 1031 carries no dollar cap and defers the full gain on investment property, and estate planning can make that deferral permanent. On a property with mixed use both provisions may apply, but the allocation rules and timing requirements are complex enough to require CPA guidance.
Frequently asked questions
Can I use Section 121 on my rental property?
Not directly - Section 121 applies to your primary residence, not a rental. But if you convert a rental into your primary residence and live there for two of the past five years, you may qualify, subject to the non-qualified use allocation rules.
What if my gain is $600K on my primary residence?
If you're married filing jointly, the first $500K is excluded under Section 121 and the remaining $100K is taxable. You can't 1031 exchange the excess, because the property is your primary residence rather than investment property. To use 1031, you'd have to convert it to a rental first.
Can I do a 1031 exchange and later claim Section 121?
Yes, but you must own the replacement property for at least five years after the exchange before Section 121 applies. You also need to meet the two-of-five-year occupancy test, and gain from non-qualified (rental) use is allocated out.