Three SEC forms cover who owns what and who just bought or sold it. They are frequently lumped together as “insider filings,” which obscures the fact that they are filed by different people, on different deadlines, for different reasons — and that only one of them reliably tells you anything.
This article is for informational and educational purposes only. It is not financial advice, investment advice, or a recommendation to buy, sell, or hold any security, cryptocurrency, or financial product. Always verify data with official sources before making financial decisions.
Short answer: three forms, three different stories
Short answer: Form 4 reports transactions by corporate insiders — officers, directors and holders of more than 10% of a class of stock — and is due within two business days. Schedule 13D is filed by anyone crossing 5% ownership who may seek to influence the company. Schedule 13G is the passive alternative to 13D, available to investors who cross 5% without intent to control. The distinction between the last two is about intent, and it is the most informative thing in either filing.
| Form | Who files | Deadline | What it signals |
|---|---|---|---|
| Form 4 | Officers, directors, 10% holders | 2 business days after the trade | A specific transaction |
| Schedule 13D | 5%+ holders with potential activist intent | Days after crossing the threshold | Possible campaign for change |
| Schedule 13G | 5%+ passive holders | Varies by filer type | Ownership without intent to control |
Form 4 and the two-business-day clock
The short deadline is what makes Form 4 the most useful of the three. A transaction becomes public within two business days, so the information is close to current — unlike the 45-day lag on quarterly institutional filings.
Every Form 4 identifies the insider and their role, the transaction date, a code describing what happened, the number of shares, the price, and the resulting total holding. That last field is the one most often skipped and most worth reading: a director selling 10,000 shares means something very different depending on whether they hold 20,000 or 2,000,000 afterward.
Transaction codes: what P, S, M, A and F really mean
The single-letter code determines whether a filing is informative or noise, and this is where most misreadings originate.
- P — Open market purchase. The insider spent their own money at market prices. The most informative code on the form, and the rarest.
- S — Open market sale. Informative, but far more ambiguous. Insiders sell for diversification, tax bills, divorce, house purchases and scheduled plans.
- M — Exercise of a derivative. Converting options into shares. A compensation event, not a market view.
- A — Grant or award. Shares received as compensation. Contains no information about the insider’s opinion.
- F — Shares withheld for taxes. The company withholds stock to cover tax on a vesting event. This appears as a disposition and is routinely miscounted as insider selling in automated coverage.
A large share of headline “insider selling” is codes M, A and F — compensation mechanics with no directional content. The research literature has consistently found that insider buying carries modest predictive power while insider selling carries very little, and the code distribution is the reason.
The 5% threshold that splits 13D from 13G
Crossing 5% of a class of registered equity triggers a filing obligation. Which form depends on why you bought.
An investor with no intention of influencing control files 13G, the shorter passive form. Index funds and large asset managers file thousands of these and they carry essentially no signal — they reflect fund flows into products that must hold the stock.
An investor who may seek board representation, a sale of the company, a capital return or a strategy change files 13D. It requires disclosing the purpose of the transaction, the source of funds, and any plans for the issuer — which is genuinely informative, because it states intent in the filer’s own words.
Activist intent and the amendment window
A 13D must be amended promptly on any material change — a meaningful change in position size, or a change in plans. Those amendments are where an activist campaign becomes visible: the original filing may say only that shares are held for investment purposes, while a later amendment discloses discussions with management or an intention to nominate directors.
An investor who files 13G and later develops activist intent must convert to a 13D. That conversion is one of the more reliable signals in the entire disclosure system, because it represents an explicit change in stated purpose rather than an inference drawn from position size.
Why 10b5-1 plan sales are the least informative trades
Form 4 includes a checkbox indicating whether a transaction was made under a Rule 10b5-1 trading plan. When checked, the sale was arranged in advance under a written plan adopted while the insider was not in possession of material non-public information.
These sales are scheduled by design. An executive who adopted a plan months earlier selling on a preset date is executing a decision made under entirely different circumstances. Following 2022 amendments, plans carry mandatory cooling-off periods before the first trade, which strengthened the separation between adoption and execution. A plan sale tells you an insider wanted diversification at some point in the past — nothing about today.
What this article does not conclude
Insider filings describe transactions and ownership, not prospects. The empirical record supports a modest edge from clustered open-market purchases by multiple insiders and very little from sales of any kind.
All three forms are available free through the SEC’s EDGAR system. Third-party aggregators that summarise them frequently fail to distinguish transaction codes, which is the single most important field on the form.