Boot, and how to avoid an accidental tax bill.

The plain word for the taxable bits

Boot is the plain term for the part of an exchange that does not qualify for deferral. It is not a penalty. It is just the slice of the deal the rules treat as cash in your pocket, and it gets taxed like a sale. There are two ways to create it, and both are avoidable if you see them coming.

Cash boot and mortgage boot

Cash boot is the simpler one. If you take some money off the table at the sale instead of rolling all of it into the next property, the part you kept is taxable. The intermediary holds the proceeds for a reason. Money that detours into your account on the way through is money you chose to recognize.

Mortgage boot is the one that surprises people. If you pay off more debt on the sale than you put on the replacement, the difference is treated as a benefit to you, and it is taxable too. You can land in mortgage boot without ever touching a dollar of cash. The shortfall in debt is enough.

The rule that keeps the gain deferred

Full deferral has two conditions, and you have to meet both. Buy a replacement worth at least what you sold. And carry at least as much debt as you paid off, or replace the missing debt with your own cash. Value at or above value, debt at or above debt, with equity allowed to stand in for debt. That is the whole test.

In that example the prices match perfectly. You still have a problem, because the new loan is 300,000 dollars lighter than the old one. Either add 300,000 of your own cash to fill the gap, or place a larger loan. Do nothing and the 300,000 is taxable.

You can land in mortgage boot without ever touching a dollar of cash. The shortfall in debt is enough.

What boot costs, and the discipline

Boot is taxed the way a sale is. Long-term capital gains on the gain, depreciation recapture on what you wrote off over the years, the net investment income tax, and your state on top. Equity can substitute for debt. Cash cannot substitute for value. Either form of boot turns a full exchange into a partial one. Sometimes that is a fine trade, made with eyes open. It should never be a trade you make by accident.

There are real reasons to accept boot on purpose. You may want some cash out, and paying the tax on that slice can be a price worth choosing. The point is never that boot is forbidden. The point is that it should be a decision, sized in advance, with the tax quantified, rather than a surprise you find when the return shows up smaller than the deferral you thought you had.