Buyback Blackout Period: When Companies Stop Buying Their Own Stock, and Why It Matters

In the twelve months to September 2025, S&P 500 companies spent a record $1.020 trillion buying back their own shares, according to S&P Dow Jones Indices. That makes companies themselves one of the largest buyers of U.S. stocks. But they are a part-time buyer. Around every earnings report, most companies stop discretionary repurchases for several weeks: the buyback blackout period. Knowing when the biggest buyer steps away, and what rules govern it when it comes back, is part of reading institutional money flow. If you are an executive, it matters twice: your own trading window usually closes at the same time.

What is a buyback blackout period?

A buyback blackout period is the time when a company pauses discretionary open-market repurchases of its own stock, usually from late in a fiscal quarter until shortly after it reports results, because it may hold material nonpublic information about those results.

The logic is the same as for employee trading. By the last weeks of a quarter, the finance team knows roughly how the quarter went, and the market doesn’t. A company buying its own stock on that knowledge would risk insider trading liability under Rule 10b-5, exactly as an executive would. So most companies close the window for discretionary repurchases, along with employee trading, until the results are public and the market has had time to absorb them.

Two points are often misunderstood. First, the blackout is company policy, not an SEC rule. No regulation sets its start or end date, so it varies from company to company. Second, a blackout stops discretionary buying. Purchases under a pre-arranged Rule 10b5-1 plan can continue, which is why many large repurchasers keep buying through earnings season.

When does the buyback blackout window start and end?

The window typically closes a few weeks before the fiscal quarter ends and reopens a day or two after earnings are released, but each company sets its own dates.

The calendar above shows one illustrative calendar-year company. Its policy closes the window about two weeks before each quarter end and reopens it two trading days after the earnings release. For a company reporting four to five weeks after the quarter ends, that is a blackout of roughly six to seven weeks each quarter. A company with a non-calendar fiscal year runs the same pattern on different dates. Because companies report at different times, the market-wide effect is a season rather than a single date: the share of companies in blackout rises through the last weeks of each calendar quarter and falls as earnings season progresses. That aggregate “buyback season” is something analysts estimate rather than observe, because companies don’t publish their windows.

Earnings season also lines up with other calendar flows. Quarter-end rebalancing by pensions and balanced funds happens just as many blackouts begin, as our guide to quarter-end rebalancing explains, and the quarterly options expiration falls in the same weeks, covered in triple witching.

What is Rule 10b-18, and what are its four conditions?

Rule 10b-18 is an SEC safe harbor for issuer repurchases: if a company meets four conditions on a given day, its purchases that day are protected from claims of market manipulation.

The conditions, from 17 CFR 240.10b-18(b), are:

1. Manner. All purchases on a single day go through only one broker or dealer.
2. Timing. The purchase is not the opening regular-way trade, and not within the last 10 minutes before the close for stocks with average daily trading volume (ADTV) of $1 million or more and public float of $150 million or more, or the last 30 minutes for other stocks.
3. Price. The price paid does not exceed the highest independent bid or the last independent transaction price, whichever is higher.
4. Volume. Total daily purchases do not exceed 25% of ADTV, except that once a week the company may make one block purchase instead, if it makes no other Rule 10b-18 purchases that day.

Two features are easy to miss. The rule says compliance is voluntary, and failing a condition does not create a presumption that the company manipulated its stock; it only means that day’s purchases are outside the safe harbor. And the rule governs how a company buys, not when it may buy given what it knows. That second question is answered by insider trading law, which is where blackouts and 10b5-1 plans come in.

How does a 10b5-1 buyback plan work during a blackout?

A 10b5-1 buyback plan lets a company keep repurchasing through its blackout, because the amount, price and timing rules were fixed in advance, when the company had no material nonpublic information.

Rule 10b5-1 gives an affirmative defense to insider trading liability when a trade is made under a binding contract, instruction or written plan adopted in good faith before the trader became aware of inside information. For a buyback, the company typically adopts the plan while its window is open: buy up to a set number of shares a day, below set price limits, over a set period. The broker then executes without further input. The SEC’s 2022 amendments added cooling-off periods for directors and officers (the later of 90 days or two business days after the next periodic report, capped at 120 days) and 30 days for other persons; the SEC fact sheet describes these as applying to persons “other than issuers,” so a company’s own buyback plan is not subject to them.

In practice, then, a company in blackout may still be buying, just mechanically. What disappears is the discretionary layer: the treasurer stepping in after a sharp drop.

How does a blackout play out, step by step?

Here is an illustrative quarter for a hypothetical company with a $20 billion annual buyback authorization and stock trading 10 million shares a day at $200.

1. Open window (January to mid-March). The company buys at its discretion. Under Rule 10b-18’s volume condition it can buy up to 25% of ADTV, or 2.5 million shares a day, about $500 million, through one broker, away from the open and the last 10 minutes.
2. Before the blackout. In early March, with the window still open, it adopts a 10b5-1 plan to buy up to 500,000 shares a day if the stock is below $210.
3. Blackout (mid-March to two days after an April 28 earnings release). Discretionary purchases stop. The 10b5-1 plan keeps buying whenever its price condition is met. On days the stock trades above $210, the company buys nothing.
4. Earnings and reopening. Results are released April 28. Two trading days later, the window reopens and discretionary purchases resume.
5. Effect on the tape. During the blackout the company’s daily bid shrinks from up to 2.5 million shares to at most 500,000, and only below $210. In a selloff, that is less support than the market saw in February.

The numbers are hypothetical, but the shape is common: buyback demand thins out around earnings, exactly when uncertainty is highest. Our analysis of Mag 7 earnings moves shows how large those post-earnings moves can be.

How does the 1% stock buyback excise tax work?

A U.S. company with publicly traded stock owes a 1% excise tax on the fair market value of stock it repurchases in a year, reduced by the value of stock it issues in that year, including to employees.

The tax is in 26 U.S.C. 4501. It applies to any domestic corporation whose stock trades on an established securities market, for repurchases after December 31, 2022. Section 4501(c)(3) reduces the taxable amount by the fair market value of stock issued during the year, which is why companies that pay a lot of stock compensation owe tax only on their net repurchases. There is a de minimis exception when total repurchases in the year are $1 million or less. S&P Dow Jones Indices estimated the tax at $2.25 billion for S&P 500 companies in the third quarter of 2025 and called it “a manageable expense” that “has not impacted overall buybacks.”

How big are buybacks, and do they support stocks?

Buybacks are one of the largest sources of demand for U.S. stocks: S&P 500 companies repurchased $249.0 billion in the third quarter of 2025 alone, per S&P Dow Jones Indices.

Do they support prices? Mechanically, a buyback adds a buyer and lowers the share count, which lifts earnings per share. S&P Dow Jones Indices reports that 312 S&P 500 companies reduced their share count year over year in the third quarter of 2025, against 160 that increased it. Whether a buyback creates value depends on the price paid. For flows, the more useful point is concentration: nearly half of all S&P 500 buybacks come from 20 companies, many of them mega-cap tech, so their blackout calendars matter for the index.

What happened to the SEC’s 2023 buyback disclosure rule?

The SEC adopted a rule in May 2023 requiring companies to disclose daily repurchase data each quarter, but the Fifth Circuit vacated it on December 19, 2023, so the earlier disclosure rules still apply.

The May 3, 2023 rule would have required companies to report daily repurchase activity, explain the objectives of their buybacks, and tick a box if officers or directors traded within four business days of a buyback announcement. The Chamber of Commerce and others challenged it. The Fifth Circuit found the SEC had acted arbitrarily and capriciously by not adequately responding to comments and not conducting a proper cost-benefit analysis, gave the agency time to fix the defects, and then vacated the rule when the SEC said it could not. As a result, according to Covington’s summary, companies follow the repurchase disclosure requirements that applied before the rule, which report monthly totals rather than daily trades. For anyone tracking buyback flows, that means the data stays quarterly and aggregated.

What does a buyback blackout mean for executives with company stock?

For an executive or employee with a concentrated position, the company’s buyback blackout and your own trading blackout usually overlap: the stock loses a buyer at the same time you lose the ability to sell.

Most insider trading policies close employee windows around the same dates, for the same reason: the company and its insiders may know the quarter’s results. That has three consequences. First, the weeks around earnings are when your stock is most likely to gap, and you can’t act during them. Second, any hedge, such as a collar, needs to be in place before the window closes, and must comply with your company’s hedging policy and Section 16. Third, the clean way to sell through blackouts is a 10b5-1 plan: adopted while the window is open, with a 90-to-120-day cooling-off period for officers and directors, and disclosed on Form 4 with the plan checkbox, as our guide to 13D, 13G and Form 4 explains.

The company’s own buyback is not a reason to hold more. It is a flow that helps on average and disappears exactly when uncertainty peaks. Your diversification plan should stand on its own.

What is a checklist for buyback blackouts?

1. Note the company’s fiscal quarter end and expected earnings date; estimate the blackout as late-quarter to two days after earnings.
2. Check the latest 10-Q or 10-K for the size of recent repurchases and remaining authorization.
3. Remember that 10b5-1 buyback plans may keep buying through the blackout, within preset limits.
4. Expect the discretionary bid to be thinnest when earnings risk is highest.
5. Remember the Rule 10b-18 limits: 25% of ADTV, no opening trade, nothing in the last 10 or 30 minutes.
6. If you are an insider, set up hedges and 10b5-1 sales while your window is open.
7. Don’t treat a buyback authorization as a guarantee of support.

Frequently asked questions

Key takeaways

1. A buyback blackout is company policy, not an SEC rule: discretionary repurchases pause from late in the quarter until after earnings.
2. Rule 10b-18 is a voluntary safe harbor: one broker a day, no opening trade or last 10/30 minutes, a price cap and 25% of ADTV.
3. A Rule 10b5-1 buyback plan lets a company keep buying through the blackout on rules set in advance.
4. The 1% excise tax under IRC §4501 applies to net repurchases after 2022; employee stock issuance reduces the base.
5. S&P 500 buybacks reached a record $1.02 trillion in the twelve months to September 2025, per S&P Dow Jones Indices.
6. For executives, your own trading window often closes when the company’s buyback pauses; plan sales and hedges ahead of time.

Sources and method

1. 17 CFR 240.10b-18 (Rule 10b-18) — issuer repurchase safe harbor conditions; voluntary, no presumption
2. 17 CFR 240.10b5-1 (Rule 10b5-1) — affirmative defense for pre-arranged trading plans
3. SEC fact sheet, Rule 10b5-1 amendments (Release 33-11138) — cooling-off periods; issuers excluded from the cooling-off requirement
4. 26 U.S.C. 4501 — 1% excise tax on repurchases, netting, $1 million de minimis, effective after December 31, 2022
5. S&P Dow Jones Indices, S&P 500 Q3 2025 buybacks (Dec. 18, 2025) — Q3 2025 $249.0B, 12-month $1.020T record, Q1 2025 $293.5B, excise tax $2.25B
6. SEC press release 2023-85 — share repurchase disclosure modernization adopted May 3, 2023
7. Covington, Court Vacates SEC’s Share Repurchase Disclosure Rule — Fifth Circuit vacatur on December 19, 2023 (secondary source)

Chart 1 is an illustrative company calendar: blackout dates vary by company policy and no SEC rule fixes them. Chart 2 summarizes 17 CFR 240.10b-18(b). Chart 3 is illustrative Proflex math under 26 U.S.C. 4501. Buyback totals are from S&P Dow Jones Indices’ December 18, 2025 release, the latest quarterly release we could verify as of October 2026. The vacatur of the 2023 disclosure rule is cited from a law-firm summary because the SEC’s rule page does not state it.