Updated July 29, 2026. Quick answer: Because a federal rule sets that floor, and it applies to your private employer. Rule 14e-1(a) provides that no person who makes a tender offer shall hold it open for less than twenty business days from the date it is first published or sent to security holders. The rule is written as “no person”, not as “no reporting company” — which is why a company with no public shares still runs a twenty-day window.
The rule, and the words that make it reach you
17 CFR §240.14e-1 opens: “As a means reasonably designed to prevent fraudulent, deceptive or manipulative acts or practices within the meaning of section 14(e) of the Act, no person who makes a tender offer shall: (a) Hold such tender offer open for less than twenty business days from the date such tender offer is first published or sent to security holders …”
Section 14(e) is an antifraud provision, and antifraud provisions are not limited to registered securities. That is the whole mechanism. The disclosure-and-filing rules for issuer tender offers are keyed to registered classes and do not reach a private company — but this timing rule does.
The second clock, which is the one that actually surprises people
Rule 14e-1(b): if the offeror increases or decreases the percentage of the class being sought, or the consideration offered, or the dealer’s soliciting fee, the offer must remain open at least ten business days from the date notice of that change is first published. So a mid-offer change to the price or the amount being bought resets a floor of its own. If your window appeared to extend for no visible reason, a change to one of those three things is the usual explanation.
| Event | Minimum the offer stays open | Rule |
|---|---|---|
| Offer first published | 20 business days | 14e-1(a) |
| Percentage sought changes | 10 business days from notice | 14e-1(b) |
| Consideration offered changes | 10 business days from notice | 14e-1(b) |
| Soliciting fee changes | 10 business days from notice | 14e-1(b) |
Business days, not calendar days. Twenty business days is about four weeks of calendar time, and more across a holiday period. The practical consequence is that the deadline in the email you received is a company-chosen date sitting on top of a federal floor — the company can run it longer, and often does, but it cannot run it shorter.
What the window is for is the decision, and the decision has a tax shape before it has a price shape — part of the check may not be capital gain at all, and which shares you tender is a separate choice with its own default.
Sources
17 CFR §240.14e-1(a) and (b); 17 CFR §240.13e-4(a)(1); 15 U.S.C. §78n(d)(1) and §78n(e). Fetched and confirmed July 2026.
This states what the cited authority says. It is not tax, legal or investment advice. A tender offer runs on documents specific to your company and your grants, and nothing here tells you whether to sell.