The short answer
For a gain you realize directly, the 180 days begin on the day the gain would be recognized for federal tax purposes, which for a property sale is the closing date and for a section 1231 gain is also the sale date. If the gain reaches you through a partnership or S corporation, the default start is the last day of the entity's tax year, and you may instead elect the entity's own sale date or the unextended due date of its return. Installment sellers can start a new window with each payment. All of these come from Reg. section 1.1400Z2(a)-1.
At a glance
| Statute | 180-day period beginning on the date of the sale or exchange |
|---|---|
| Direct sale | The day the gain is recognized, normally the closing date |
| Section 1231 gain | Same rule: the sale date, not year-end |
| Partner or S shareholder | Default: last day of the entity's tax year |
| Partner elections | The entity's sale date, or its return due date without extensions |
| Installment sale | Each payment date, or the last day of the tax year |
| REIT capital gain dividend | Year-end by default, or the dividend date by election |
| Hypothetical | Closing October 15, 2026 → invest by April 12, 2027 |
The default rule ties the window to the day the gain is recognized
Section 1400Z-2(a)(1)(A) defers gain to the extent you invest 'in a qualified opportunity fund during the 180-day period beginning on the date of such sale or exchange.' The regulation restates that as a period that 'begins on the day on which the gain would be recognized for Federal income tax purposes' if no deferral election were made.
For a closing on a building, that is the day the sale is complete for tax purposes, usually when the deed and funds are exchanged. For stock, the regulation's first example says the window starts on the trade date, not the settlement date.
Section 1231 gain from business real estate follows the same rule. The regulation limits eligible 1231 gain to the amount above any ordinary-income recapture and points to the general 180-day rule, so the window starts on the sale date. Which part of a rental gain is eligible is the subject of using 1031 funds in an opportunity zone fund.
Partners, S corporation shareholders and installment sellers have later start dates
When a partnership sells and does not defer the gain itself, the partner's window 'generally begins on the last day of the partnership taxable year' in which the partner's share is taken into account. The partner may instead elect to use the partnership's own 180-day period, or a period 'beginning on the due date for the partnership's tax return, without extensions.' Rules analogous to these apply to S corporations, nongrantor trusts and estates.
For gain reported on the installment method, you may treat 'the date the payment on the installment sale is received or the last day of the taxable year' as the start, and if you use payment dates, 'each payment will begin a new 180-day period.'
Capital gain dividends from a REIT start on the last day of your tax year unless you elect the distribution date, in which case the eligible amount is limited to the capital gain dividends reported to you.
Worked example: three start dates from the same year
Hypothetical dates; confirm your own with your CPA. You close the sale of a rental on October 15, 2026. Counting that day as day one, your 180th day is April 12, 2027.
You are also a partner in a calendar-year partnership that sold a building on June 1, 2026 and did not defer. By default your window starts December 31, 2026 and ends June 28, 2027. Elect the partnership's own window and it ended November 27, 2026; elect the due-date rule and it starts March 15, 2027 and ends September 10, 2027.
The choice affects more than convenience. A 2026 sale invested in 2027 falls under the amended rules for amounts invested after December 31, 2026, while an investment made in 2026 falls under the original statute, whose deferral ends on December 31, 2026. How the two deferral periods compare is in the rolling five-year deferral.
A failed or partial 1031 exchange starts the clock when the boot gain is recognized
Boot or a failed exchange produces gain on the day it would be recognized, which is usually the sale date of the relinquished property. If the intermediary pays you in the following tax year, Reg. section 1.1031(k)-1(j)(2) can put that gain on the installment method, and the installment rule above then lets the payment date start the window.
Two cautions apply. Ordinary recapture under section 1245, common after a cost segregation study, is not eligible gain at all. And money still held by the intermediary is not available to invest before the exchange period ends, so check that the 180 days have not run out before it is released; see when the QI releases my money.
The reporting of the deferral itself is covered in opportunity zone fund reporting requirements.
What to do now, and where the client's fund route fits
Write down the recognition date for each gain, the entity's tax year and return due date for any flow-through gain, and the payment schedule for any installment sale. Then pick the start date that gives you the most time without pushing the investment into the regime you do not want.
Opportunity zone funds are one of the deferral routes we place, alongside exchanges; the basics are on our opportunity zone page and a worked client scenario is in the opportunity zone case study. Fund investments are illiquid and carry real estate and development risk, so review the offering documents and the law changes in opportunity zones after the 2025 act with your adviser.
Related questions
Is the day of closing day one or day zero?
The statute says the period begins on the date of the sale, so the closing date is generally treated as day one. Confirm the count with your adviser rather than investing on the last day.
Does a K-1 gain always use year-end?
Year-end is the default. A partner may elect the partnership's own 180-day period or one beginning on the partnership return's unextended due date.
Can each installment payment start a new window?
Yes. If you treat payment dates as the start, each payment begins a new 180-day period for the gain in that payment.
Is the start date different for a section 1231 gain?
No. The current regulation points 1231 gain to the general rule, so the window starts on the sale date.
Did the July 2025 tax act change the 180 days?
The 180-day language in section 1400Z-2(a)(1)(A) was not changed; the act changed deferral and basis rules for amounts invested after December 31, 2026.
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.