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Full deferral needs three things: buy up, reinvest every dollar, replace the debt.
A 1031 exchange defers 100% of your gain only if three conditions hold: the replacement costs at least as much as what you sold, every dollar of equity goes back in, and the new debt is at least the old debt. Miss any one and the difference is "boot" — taxable now, with depreciation recapture at 25% hitting the boot before anything else. Most online calculators show only the cash side and miss mortgage boot entirely; this one shows both, plus the number investors actually need next: your new basis in the replacement property, which is where the deferred gain quietly lives until a taxable sale or the step-up at death.
Investors use it before listing the rental: the three-condition test for full deferral (buy up, reinvest all equity, replace the debt), the mortgage boot nobody warns about, and the new basis that carries the deferred gain — because day 46 without an identification kills the whole exchange.
Anything of value you receive that isn't like-kind real property: cash left over after reinvestment, AND net mortgage relief — if your old loan was $300,000 and the new one is $250,000, that $50,000 of debt reduction is taxable boot even if you reinvested every cash dollar. Recognized gain is the lesser of your total realized gain or total boot. You can offset mortgage boot by adding cash, and offset cash boot by taking on more debt.
45 calendar days from the sale to identify replacement properties in writing (up to 3 at any value, or more under the 200% rule), and 180 calendar days to close — both absolute, running simultaneously, no extensions. A qualified intermediary must hold the proceeds the whole time; if the money touches your account, the exchange is dead and the full gain is taxable. Note: if the 180th day falls after your tax return due date for the sale year, you must file an extension to preserve it.
Once, at death: heirs take the property at stepped-up basis and the deferred gain — including decades of depreciation recapture — disappears. That's the "swap 'til you drop" strategy: chain exchanges indefinitely (there's no limit), never sell, and let the step-up erase the bill. Every other exit — a taxable sale, a failed exchange, moving into the property too soon — eventually collects the deferred gain plus recapture through the reduced basis this calculator shows.