Timeline rules

Everything else in a 1031 exchange has some give. The timeline has none. The 45-day and 180-day deadlines are hard, they start the moment you sell, and blowing either one by a single day makes the entire gain taxable. More failed exchanges trace to the calendar than to any other rule, and almost always because the investor misunderstood how the two clocks relate. This page is that relationship, in full.

Both clocks start on the sale date, and run together

The most important thing to understand, and the most commonly gotten wrong, is that the two periods begin on the same day and run concurrently. The day you close the sale of your relinquished property, both clocks start.

From that day, you have 45 days to identify your replacement property, and 180 days to close on it. The 45 days are not a separate front-end period followed by 180 more. The 45-day window sits inside the 180-day window. So if you take the full 45 days to identify, you have 135 days left to close, not 180. Every day you spend deciding is a day subtracted from your closing window. Investors who assume they have 45 plus 180, a total of 225 days, are working from a deadline that does not exist and can miss the real one badly.

The 45-day and 180-day periods both start on your sale date and run concurrently, so the identification time you use is subtracted from your closing time, not added to it.

Day 45: identify in writing

By midnight on day 45, you must identify your replacement property in a signed written document delivered to your qualified intermediary. Not a handshake, not an intention, a written, signed identification with enough detail (a legal description or unambiguous address) to specify exactly which property.

This deadline is treated as absolute. There are no general hardship extensions; the only relief is for federally declared disasters affecting your area, which the IRS announces case by case. Miss day 45, and the exchange is over. This is the single most commonly missed deadline in all of 1031, usually because an investor could not find a replacement property in time and let the clock run rather than identifying a fallback.

By day 45 you must deliver a signed, written identification of your replacement property to your intermediary, with no extensions except for declared disasters.

Day 180: close, unless your tax return is due sooner

By day 180, you must close on one of the properties you identified. Also absolute, also no hardship relief. But there is a hidden shortener that catches late-year exchanges.

The rule is actually “180 days or the due date of your tax return for the year of the sale, whichever is earlier.” So if you sell in, say, November, your 180 days would run into the following May, but your tax return is due in April, which comes first. In that case your exchange period is cut short unless you file an extension for your return, which restores the full 180 days. This is a real trap for fourth-quarter sales, and the fix, filing an extension, has to be done deliberately.

The 180-day deadline is cut short if your tax return due date comes first, so a late-year exchange usually requires filing a tax extension to preserve the full period.

Why the identification deadline drives everything

Because the two clocks are linked, the 45-day identification deadline is the real pressure point of the whole exchange. It forces you to know your replacement property early, which is why experienced exchangers line up candidate properties before they ever sell, and why reverse and improvement exchanges exist, to relieve the timing squeeze. The identification rules themselves, how many properties you can name and the value limits, are their own subject on the identification rules page. The point here is that the calendar, not the paperwork, is what most often kills a deferral, and it is entirely avoidable with preparation.

The bottom line

• The 45-day and 180-day clocks both start on your sale date and run concurrently.
• Identification time you use is subtracted from your closing time; there is no separate 45-plus-180.
• By day 45, deliver a signed written identification to your intermediary; no extensions but declared disasters.
• By day 180, close, unless your tax return due date comes first, which an extension can fix.
• The calendar kills more exchanges than any other rule, and preparation before you sell is the fix.

For how many properties you may name, read identification rules. For the structures that relieve the time squeeze, see reverse exchanges. For the full picture, start at the 1031 exchanges and exit planning hub.

Last verified August 2026.