The short answer
Usually very little. Your identification and exchange periods start on the date you actually transfer the property under Reg. section 1.1031(k)-1(b)(2), not on any date typed into the exchange agreement, so a one-week slip moves both deadlines a week later automatically. Tell the intermediary, let it update the closing instructions, and make sure the written notice of assignment still reaches the buyer on or before the new closing day. Two situations need more care: a closing that slips into a new tax year, and a reverse exchange, where the 180-day clock is already running.
At a glance
| Clock start | The date the property is actually transferred |
|---|---|
| Day 45 | Midnight on the 45th day after the transfer |
| Day 180 | 180 days after the transfer or the return due date, whichever is earlier |
| Assignment notice | Must reach all parties on or before the actual closing |
| Year-end slip | Moves the sale, and any failed-exchange gain, into the new tax year |
| Return due date | April 15 for individuals, extendable six months |
| Reverse exchange | 180 days run from the titleholder's acquisition and do not move |
The deadlines follow the transfer, so they move with the closing
Reg. section 1.1031(k)-1(b)(2) starts the identification period 'on the date the taxpayer transfers the relinquished property' and ends it 'at midnight on the 45th day thereafter'. The exchange period starts on the same date and ends on the earlier of the 180th day or the due date, with extensions, of your return for the year of the transfer. Paragraph (b)(2)(iv) says property is transferred when it is disposed of under section 1001(a).
Nothing in that rule refers to the exchange agreement. If the agreement or a cover letter lists projected deadlines, they are estimates; the legal ones are recalculated from the real closing. Ask the intermediary to confirm the new dates in writing so everyone works from the same calendar. When the transfer date itself is unclear, see when the 45-day clock starts.
The statute is built the same way. Section 1031(a)(3) counts 45 days and 180 days from 'the date on which the taxpayer transfers the property relinquished in the exchange'. A later closing therefore shifts your 45 days intact. The 180 days shift too, unless a closing that moves from mid-October into later autumn runs them past April 15 of the next year, where the return due date cuts them short.
Three documents may need a quick update
Most exchange agreements are not tied to a specific closing date, but read yours, because a few recite one. The documents that usually matter are these.
- Closing instructions: the intermediary's letter to the closing agent naming it as payee of the net proceeds should carry the right file and closing date.
- Notice of assignment: paragraph (g)(4)(v) needs written notice to all parties 'on or before the date of the relevant transfer'. A notice already delivered still works; if it was not yet sent, it must go out before the new date.
- Replacement contract: if your purchase is timed off the sale, check its closing and contingency dates against the new day 45 and day 180.
Worked example: a December 26 closing that slips to January 2
Hypothetical dates; run your own with your CPA. With a December 26, 2026 closing, day 45 is February 9, 2027 and day 180 would be June 24, 2027. But your 2026 return is due April 15, 2027 under section 6072, so the exchange period ends then unless you file for the automatic six-month extension under Reg. section 1.6081-4. The fix is covered in filing an extension to keep the full 180 days.
If the closing slips to January 2, 2027, day 45 becomes February 16 and day 180 becomes July 1, 2027. The return for the year of the sale is now the 2027 return, due in April 2028, so the due-date trap disappears and no extension is needed.
The slip also moves the sale itself into 2027. If the exchange later fails or leaves boot, that gain belongs to the 2027 return, at 2027 rates and thresholds. The planning around that boundary is in the 1031 tax-year straddle and Q4 and tight deadlines.
In a reverse exchange the clock is already running, so a delay costs days
Reverse exchanges work the other way. Under section 4.02 of Rev. Proc. 2000-37, the relinquished property must be identified within 45 days and transferred within 180 days of the titleholder's acquisition, and the combined parking period 'does not exceed 180 days'.
A one-week slip on your sale does not extend any of that; it eats a week of the time left. If the sale is slipping toward day 180, talk to the titleholder and your attorney at once, because the safe harbor has no extension. The structure is in the reverse 1031 exchange guide.
If the slip is really a collapse, the paperwork question changes
A week is a delay. A buyer who walks away is a different problem: no transfer means no exchange period, and the exchange agreement simply waits or is terminated under its own terms. What happens to fees and documents then is in what happens if my sale falls through.
A later closing also gives you more calendar time to line up replacements. If you plan to name a Delaware Statutory Trust interest as a backup on your identification notice, confirm the new day 45 with your intermediary and ask your CPA or attorney to check the dates before you sign the notice.
Related questions
Do I need to sign a new exchange agreement?
Usually not. The agreement governs the relationship, and the deadlines come from the regulation. Sign an amendment only if your agreement recites a closing date that the intermediary wants corrected.
I already sent my identification list. Is it still valid?
The regulation measures identification from the transfer date. Ask your intermediary whether a list delivered before the sale closed was accepted, and resend it after closing if in doubt, well before the new day 45.
Does the buyer need a new notice of assignment?
Not if the existing notice was delivered on or before the actual closing. If the contract was amended to a new buyer entity, that party needs notice too.
Can I ask the intermediary to treat the original date as the start?
No. The periods run from the actual transfer under Reg. section 1.1031(k)-1(b)(2), and no agreement can change that.
What if my closing slips from late December into January?
The sale moves into the new tax year, and the return-due-date limit no longer cuts short your 180 days; see the worked example above.
Sources
Checked against these publications on September 30, 2026. Rules and figures change; confirm the current version with your CPA or attorney before you act. This page is general information, not tax or legal advice.