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Cash Boot vs. Mortgage Boot: A Plain-English Guide

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Sarah Chen
Tax Strategy, zoom1031
May 5, 2026 · 5 min read

Boot is any non-like-kind property received in a 1031 exchange. Even $1 of boot can trigger partial taxation. Here's exactly how to calculate your exposure before you close.


"Boot" is one of those 1031 exchange terms that every investor has heard but very few can calculate correctly. It matters because even $1 of boot can trigger a partial taxable event — and not knowing your boot exposure before closing can lead to an unexpected tax bill in April.

Here's a plain-English breakdown of what boot is, how to calculate it, and how to minimize it.

What Is Boot?

Boot is anything of value you receive in a 1031 exchange that is not like-kind real property. The IRS taxes boot in the year of the exchange, even if the rest of the exchange qualifies for full deferral.

There are two types: cash boot and mortgage boot. Both can exist in the same exchange, and they interact in ways that aren't always intuitive.

Cash Boot

Cash boot is the simpler of the two. It occurs when you receive cash out of the exchange — either directly or because you don't reinvest all of your net sale proceeds into the replacement property.

Example: You sell a rental property for $800,000. After paying off your $200,000 mortgage and $40,000 in closing costs, your net exchange proceeds are $560,000. If you buy a replacement property for $700,000 but only bring $510,000 from the exchange (keeping $50,000), that $50,000 is cash boot and it's fully taxable.

To avoid cash boot: reinvest 100% of the net proceeds from the relinquished sale. Every dollar that doesn't go into the replacement property is taxable.

Mortgage Boot (Debt Relief Boot)

Mortgage boot is more subtle and catches far more investors off guard. It occurs when the debt on your replacement property is lower than the debt on your relinquished property.

Example: You sell a property carrying a $500,000 mortgage and buy a replacement property with only a $300,000 mortgage. You've been "relieved" of $200,000 in debt — and the IRS treats that relief as if you received $200,000 in cash. It's taxable.

This happens even if you reinvested every dollar of your cash proceeds. Mortgage boot is calculated on the difference in debt, not on cash flows.

How to Calculate Your Total Boot Exposure

Total boot is the sum of cash boot and mortgage boot, netted against any additional cash you bring to the replacement purchase:

  • Cash boot = Net exchange proceeds not reinvested in replacement property
  • Mortgage boot = Old mortgage balance minus new mortgage balance (if positive)
  • Offset = Additional cash you personally contribute to the replacement purchase
  • Taxable boot = Cash boot + Mortgage boot − Offset
Boot exposure is fully calculable before you identify a replacement property. Run the numbers early — not at closing.

Offsetting Mortgage Boot with Cash

Cash boot and mortgage boot can offset each other in one direction: extra cash you bring to the replacement purchase reduces your mortgage boot dollar-for-dollar.

Using the example above: $200,000 in mortgage boot. If you contribute an additional $200,000 of personal cash to the replacement purchase (on top of your exchange proceeds), the mortgage boot is fully offset and you owe zero tax.

However, the offset does not work in reverse — mortgage boot cannot offset cash boot. Paying down more debt doesn't let you take cash out of the exchange tax-free.

The Equal-or-Greater Rule

The cleanest way to ensure zero boot is to follow this three-part rule:

  1. Purchase a replacement property worth at least as much as the relinquished property's net sale price
  2. Take on equal or greater debt on the replacement property
  3. Reinvest 100% of the net exchange proceeds

If you satisfy all three conditions, your boot exposure is zero and the entire gain is deferred.

Boot and Depreciation Recapture

One important nuance: when you do have taxable boot, the character of that income matters. Boot is first applied to reduce any recognized gain. If you have depreciation on the relinquished property, that depreciation recapture is taxed at 25% before the capital gain rate applies.

Your tax advisor can help you understand the after-tax cost of a given amount of boot — it varies significantly depending on your holding period, your depreciation history, and your state of residence.

zoom1031's Net Exchange Value Calculator

When you open an exchange on zoom1031, our portal automatically calculates your net exchange value, estimated boot exposure based on your identified replacement properties, and the minimum replacement price required to achieve zero boot. No spreadsheets. No surprises at the closing table.

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