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How to Read an SEC Form 4: Insider Trading Filings Explained

By the Stock Alerts team · Published July 17, 2026 · 8 min read

When a company's CEO buys a million dollars of stock on the open market, the law requires them to tell the public about it within two business days. That disclosure is a Form 4 — and once you know how to read one, it becomes one of the most information-dense documents in public markets. This guide walks through the form box by box.

What is a Form 4, and who has to file one?

Section 16 of the Securities Exchange Act of 1934 requires certain people connected to a public company — its officers, its directors, and any shareholder who beneficially owns more than 10% of a class of its stock — to report their transactions in that company's securities to the SEC. These people are collectively called "insiders" in the legal sense, which has nothing to do with illegal insider trading. Legal insider trading is reported; illegal insider trading is trading on material non-public information, which is prohibited whether or not you're a Section 16 insider.

The reporting happens on three related forms:

Form 3 — the initial statement of ownership, filed within 10 days of becoming an insider. It says "here is what I own as of today."
Form 4 — the workhorse. Filed within two business days of almost any change in ownership: a purchase, a sale, an option exercise, a grant, a gift.
Form 5 — an annual catch-up for a few transaction types that are allowed to be deferred, filed within 45 days of the company's fiscal year end.

Because of the two-day deadline, Form 4s are close to real-time. When you see a filing dated Tuesday for a trade executed Monday, you are seeing what an insider did with their own money essentially as it happens.

The anatomy of the form

Every Form 4 has the same structure. The header identifies the reporting person (the insider), the issuer (the company and its ticker), and the insider's relationship to the company — director, officer (with title), 10% owner, or other. Below the header sit two tables:

Table I — non-derivative securities

This is where ordinary stock transactions live, and it's usually the table that matters. Each row reports:

Transaction date — when the trade happened (not when it was filed).
Transaction code — a single letter describing what kind of transaction it was (more on this below).
Amount of securities — how many shares, and whether they were acquired (A) or disposed of (D).
Price — the price per share. For open-market trades executed at multiple prices, filers often report a weighted average with a footnote giving the range.
Securities owned following the transaction — the insider's total holding after the trade. This is the single most underrated field on the form, because it lets you compute what fraction of their stake the insider just bought or sold.
Ownership form — direct (D) or indirect (I), e.g. shares held through a trust, a family member, or an LLC.

Table II — derivative securities

Options, restricted stock units, warrants, and convertible securities are reported here, along with their exercise prices, expiration dates, and the number of underlying shares. A stock option grant shows up in Table II; the shares that appear when the option is exercised show up in Table I.

Transaction codes: the single most important letter on the form

The transaction code tells you why the shares moved, and it is the difference between a signal and noise:

Code	Meaning	How to read it
P	Open-market or private purchase	The insider chose to spend their own cash on the stock. The strongest and most-watched code.
S	Open-market or private sale	The insider sold. Meaningful, but sales have many innocent explanations (taxes, diversification, tuition).
A	Grant or award	Compensation, not a decision to invest. Usually noise for signal purposes.
M	Option exercise	Converting options into shares. Often paired with an S row when shares are sold to cover the cost.
F	Shares withheld for taxes	The company withheld shares to cover tax on vesting equity. Routine.
G	Gift	A bona fide gift — to family, a trust, or charity. No price is paid.
C	Conversion of a derivative	Converting one security into another, e.g. preferred into common.
D	Disposition back to the company	Sale of shares back to the issuer.
J	Other	Anything that doesn't fit — always explained in a footnote. Read the footnote.

Rule of thumb: a Form 4 headline saying an executive "sold $2M of stock" means very little until you check the code. An S following an M on the same day is usually just an option exercise being monetized — a compensation event, not a view on the stock. A standalone P at market prices is an insider volunteering their own cash.

What makes an insider trade meaningful?

Researchers and professional investors who study Form 4 data tend to weigh the same handful of factors:

Purchases over sales. There is one reason to buy — you expect the stock to go up — and a dozen reasons to sell. Academic work has consistently found that insider purchases carry far more predictive information than sales. We cover this in depth in Insider Buying vs. Selling.
Size relative to existing holdings. A $100,000 buy from an officer who owns $200,000 of stock is a 50% increase in their position — a real commitment. The same buy from a founder holding $500 million is a rounding error. The "shares owned following transaction" column makes this math possible.
Cluster buying. Several insiders buying in the same window is a materially stronger signal than one. Independent people reaching the same conclusion with their own money is hard to dismiss.
Who is buying. CFOs and CEOs see the whole picture; a director may not. Purchases by officers with financial visibility tend to be watched most closely.
10b5-1 plans. Many insider sales (and some purchases) are executed under pre-arranged Rule 10b5-1 trading plans, set up months in advance. Form 4s include a checkbox indicating a 10b5-1 transaction. Plan trades are scheduled, not discretionary — treat them accordingly.

Reading a real filing: a worked example

Suppose a Form 4 for ticker XYZ shows: reporting person Jane Smith, relationship "EVP, Chief Financial Officer"; Table I has one row — transaction date Monday, code P, 20,000 shares Acquired at $14.85, with 65,000 shares owned following the transaction, ownership form D.

Decoded: the CFO spent roughly $297,000 of her own money on the open market, increasing her direct stake by about 44% (from 45,000 to 65,000 shares). No 10b5-1 box checked, no offsetting option exercise. That is the profile of a discretionary, conviction-driven purchase — exactly the kind of filing that insider-tracking screens are built to surface.

Where to find Form 4s

Every Form 4 is public the moment it's accepted by the SEC's EDGAR system. You can read the raw filings at sec.gov, but raw EDGAR is not built for browsing. Our insider trades dashboard ingests filings as they hit EDGAR, decodes the tables and transaction codes into plain English, computes trade value and stake changes, and links every article back to the original document so you can verify it yourself.

Common pitfalls

Ignoring footnotes. Footnotes carry price ranges, plan disclosures, and explanations for J codes. Experienced readers check them first.
Confusing filing date with trade date. Amendments (Form 4/A) can be filed long after the original trade. Always anchor on the transaction date.
Treating grants as buys. Code A rows show up as "acquisitions" but nobody paid market price for them. Screens that don't filter by code overstate insider buying dramatically.
Assuming every sale is bearish. Executives are routinely paid in stock; selling some is how equity compensation becomes groceries. Look for sales that are unusual in size or timing, not sales per se.

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Not investment advice. This article is for educational purposes only. Stock Alerts does not provide financial, investment, or legal advice, and insider filing data is not a recommendation to buy or sell any security. Past performance is not indicative of future results.