How to read SEC Form 4 insider filings

01What Form 4 is

SEC Form 4 is the public document a company insider must file when their ownership of the company's stock changes — a purchase, a sale, an option exercise, a grant, or a gift. The requirement comes from Section 16(a) of the Securities Exchange Act of 1934, and the filings are free to read on the SEC's EDGAR system. Because insiders know their business better than anyone outside it, Form 4 is one of the few windows into what the people running a company are doing with their own money.

02Who files, and when

Three groups count as Section 16 insiders:

• Directors of the company.
• Officers — the CEO, CFO, and other designated executive officers.
• Beneficial owners of more than 10% of a registered class of the company's equity.

A Form 4 is generally due within 2 business days of the transaction — a deadline shortened from as long as 40 days by the Sarbanes-Oxley Act of 2002, which is what made insider filings timely enough to be useful. Two sibling forms complete the picture: Form 3 (an insider's initial holdings, due within 10 days of becoming an insider) and Form 5 (an annual catch-up for certain exempt transactions, due within 45 days of fiscal year-end).

Since 2023, Form 4 also carries a Rule 10b5-1 checkbox: it marks trades made under a pre-arranged trading plan the insider adopted in advance. A checked box means the sale was scheduled months earlier — materially different information than a discretionary trade made that week.

03The transaction codes

Each line of a Form 4 carries a one-letter transaction code. A few codes do most of the work:

• P — open-market purchase. The insider spent their own cash to buy stock at market prices. The most information-rich code on the form.
• S — open-market sale. The insider sold at market prices. Meaningful, but with many innocent explanations (see below).
• A — grant or award. Compensation, not a decision to invest.
• M — option exercise, and F — shares withheld for taxes. Routine mechanics of equity compensation; an M followed by an S the same day is usually an exercise-and-sell, not a change of conviction.
• G — gift. A transfer, often for estate or charitable planning.

Reading the codes matters because raw "insider selling" headlines routinely count compensation mechanics (A, M, F) as if they were conviction trades. Filtering to open-market P and S transactions is the first step of any serious read.

04Buys vs sells as evidence

The academic literature on insider trading disclosures has a consistent shape:open-market purchases carry more information than sales. An insider has exactly one reason to buy their own stock with their own cash — they expect it to be worth more — but many reasons to sell: diversification, taxes, a house, a divorce, a scheduled 10b5-1 plan.

Two patterns are widely watched. Cluster buying — several different insiders buying within a short window — is stronger evidence than a lone purchase, because independent decisions point the same way. And size relative to existing holdings matters: a CEO adding 30% to their stake is a different statement than one adding 0.3%.

05What Form 4 cannot tell you

Insider activity is context, not a verdict. Insiders are frequently early — buying into declines that continue — and their information advantage is about the business, not the stock price or the macro environment. Illegal trading on material non-public information is prohibited regardless of disclosure, so Form 4 shows you legal conviction, not certainty. A quiet period with no filings tells you almost nothing at all.

06Where to read filings free

Every Form 4 is public on the SEC's EDGAR system — browse by company or search across filings at sec.gov/edgar/search. No subscription is required; the data is public domain.

07How bips·ai uses this

bips·ai's insider activity view summarizes open-market buying and selling from Form 4 filings — filtered to the codes that carry information, flagged for 10b5-1 plans, and linked back to the original filing on SEC EDGAR — as one input among several in the bull and bear cases it builds for a ticker. It never turns a filing into a buy or sell recommendation.

This guide is for educational purposes only and is not investment advice. See the fullDisclaimers.