1031 Exchange Calculator — capital gains tax deferral estimate

A 1031 exchange calculator tells you, in dollars, how much capital gains tax you can defer by rolling the proceeds from an investment property sale into a new "like-kind" property instead of cashing out. Named after Section 1031 of the Internal Revenue Code, this strategy has been used for decades by real estate investors to keep growing a portfolio without handing a chunk of every sale straight to the IRS along the way.

This tool, built by Arb Digital as part of our free suite of real estate calculators, walks through the exact mechanics: your realized gain, how much of that gain (if any) becomes immediately taxable "boot," how much gets deferred into the new property, and what your new cost basis looks like going forward. It's meant to give you a fast, realistic estimate before you talk numbers with a qualified intermediary or CPA — not to replace either of them.

What This 1031 Exchange Calculator Does

Enter the sale price and adjusted basis of the property you're giving up, your selling costs, the purchase price of the replacement property, the mortgages being paid off and taken on, and any cash you plan to pull out of the deal. The calculator computes your total realized gain, isolates the portion that's immediately taxable because it wasn't reinvested (the boot), shows the gain you've successfully deferred, and estimates the dollar amount of tax that deferral is worth at your chosen rate. It also calculates your new adjusted basis in the replacement property, which matters enormously for any future sale.

How to Use It

1. Enter the sale price of the property you're relinquishing — the gross contract price before costs.
2. Enter your adjusted cost basis — generally your original purchase price plus capital improvements, minus depreciation taken over the years.
3. Enter your selling costs — commissions, title fees, and other transaction expenses.
4. Enter the replacement property's purchase price and the old and new mortgage balances involved.
5. Enter any cash you're taking out of the exchange rather than reinvesting, and an estimated combined tax rate.
6. Click Calculate to see your deferred gain, taxable boot, and estimated tax savings.

The Formula / How It's Calculated

Realized gain is the sale price minus selling costs minus your adjusted basis. "Boot" is anything of value you receive from the exchange that isn't like-kind real estate — most commonly cash you keep, or a reduction in your mortgage debt that isn't offset by taking on new debt of at least equal size. The calculator adds your cash taken out to any positive mortgage relief (old mortgage paid off minus new mortgage, if that number is positive) to get total boot. Your taxable gain is whichever is smaller: the realized gain or the boot. Everything above that is deferred gain, and your new basis in the replacement property is its purchase price minus the deferred gain.

The authoritative source on how this all works is the IRS guidance on like-kind exchanges under Section 1031, which confirms that gain is deferred, not eliminated — it's baked into your lower basis and will eventually be taxed, typically when you sell without doing another exchange.

The 45-Day and 180-Day Deadlines Nobody Gets a Second Chance On

The single biggest way investors blow a 1031 exchange isn't the math — it's the clock. From the day your relinquished property closes, you have exactly 45 calendar days to formally identify potential replacement properties in writing, and exactly 180 calendar days (not 180 business days) to close on one of them. These deadlines run concurrently, they include weekends and holidays, and the IRS grants essentially no extensions outside of federally declared disaster relief. Miss either one and the entire exchange collapses into a plain taxable sale, with the full gain due in that tax year.

Because 45 days goes by fast — especially in a competitive market — experienced exchangers start scouting replacement candidates before their current property even closes. The identification rules also limit how many properties you can name (commonly up to three, regardless of value, or more under certain value-based rules), so the list has to be specific and submitted in writing to your qualified intermediary, not just a mental shortlist.

The Qualified Intermediary: Why You Can Never Touch the Cash

A 1031 exchange only works if you never take actual or "constructive" receipt of the sale proceeds. That's why every exchange runs through a qualified intermediary (QI) — an independent third party who holds the funds in escrow between the sale of your old property and the purchase of the new one. If the money passes through your hands, or even sits briefly in an account you control, the exchange is disqualified retroactively and the full gain becomes taxable immediately. Choosing a QI isn't a formality; it's the structural backbone that makes the whole strategy legal. Most title companies and 1031 specialty firms can set one up, and the intermediary agreement needs to be in place before your relinquished property closes, not after.

Trading Equal-or-Up to Avoid Boot

The cleanest way to defer 100% of your gain is to follow the "equal or up" rule: buy a replacement property with a purchase price at or above what you sold, and reinvest all of your net equity, replacing at least as much mortgage debt as you paid off (or covering the gap with cash). Fall short in either price or debt replacement and you create boot — taxable in the current year even though the rest of the exchange is otherwise valid. This is exactly why the calculator above separates "boot" from "deferred gain": it's entirely possible to do a legitimate 1031 exchange and still owe some tax that same year, simply because the numbers didn't fully replace what was sold.

A common mistake is assuming that reinvesting the cash proceeds alone is enough. Mortgage relief counts too — if you pay off a $150,000 loan on the old property but only take on $100,000 of new debt, that $50,000 difference is treated as boot unless you cover it with additional cash into the deal.

Swap Till You Drop: The Long Game

Because 1031 exchanges only defer gain rather than eliminate it, many long-term real estate investors use a strategy nicknamed "swap till you drop." They keep exchanging one investment property for another — deferring gain again and again over years or decades — and never trigger the deferred tax bill during their lifetime. When the investor passes away, IRS rules currently allow heirs to inherit the property at a stepped-up basis equal to its fair market value on the date of death, which can wipe out the entire deferred gain for income tax purposes. It's a legal, well-established estate planning technique, but it depends on current step-up-in-basis rules that Congress has debated changing, so it's worth revisiting the strategy with a tax professional periodically rather than assuming today's rules will apply decades from now.

Common Mistakes to Avoid

• Touching the sale proceeds directly instead of routing them through a qualified intermediary — this alone disqualifies the exchange.
• Missing the 45-day identification window because replacement shopping didn't start early enough.
• Buying "down" in price or debt without realizing the shortfall creates taxable boot.
• Confusing "like-kind" with "identical." Real estate held for investment or business use generally qualifies for exchange against other real estate, even a different property type, as long as both are held for investment or business purposes.
• Forgetting depreciation recapture, which is taxed differently than the underlying capital gain and isn't always fully deferred in every structure — get specific numbers from a CPA.
• Assuming the exchange erases the gain rather than deferring it into a lower basis that will eventually be taxed unless offset by a future exchange or a step-up at death.

Related Free Tools From Arb Digital

If you're weighing a 1031 exchange against a straight sale, compare the numbers with our capital gains tax calculator and our home sale proceeds calculator. Investors evaluating a flip instead of a hold should check our fix and flip calculator and 70% rule calculator, and anyone budgeting the sale side should run our closing cost calculator. Explore the rest of our free online tools hub for more.

Frequently Asked Questions

This tool provides general estimates for educational purposes only and is not financial, tax, legal, or medical advice. Figures are illustrative; consult a licensed professional for decisions.