SEC Form 4: What insider transaction filings actually tell you
Form 4 is the single most-watched insider filing in US public markets. When a CEO buys shares with their own money, or a CFO sells right before earnings, that information lands on EDGAR — usually within 48 hours of the trade. Form 4 is how you find out.
Who has to file a Form 4
Section 16 of the Securities Exchange Act of 1934 requires three groups of people to file Form 4 within two business days of any trade in their company's stock: directors, executive officers, and any shareholder who owns more than 10% of a class of registered equity.
These insiders file directly with the SEC via EDGAR. The form lists the transaction date, number of shares, price, type of transaction (purchase, sale, gift, option exercise), and the insider's new total holdings after the transaction.
The transaction codes that matter
Form 4 uses a single-letter code in column 3 to describe the transaction type. The two codes that move stock prices are:
P — open-market purchase. The insider used their own cash to buy shares at the prevailing market price. This is the bullish signal. Open-market buys are rare because insiders have many ways to acquire stock (options, RSUs, ESPPs); a P-coded purchase means they specifically chose to put cash in.
S — open-market sale. Sales are noisier than buys: insiders sell for diversification, tuition, taxes, or because their 10b5-1 plan triggered. A single S code doesn't necessarily mean the insider is bearish.
Other common codes — A (grant), M (option exercise), F (tax withholding) — are usually compensation-related and not directional signals.
Why open-market buys are the high-signal data
Academic research (Jeng, Metrick & Zeckhauser 2003; Cohen, Malloy & Pomorski 2012) consistently finds that insider purchases — not sales — predict future excess returns. The mechanism is intuitive: insiders sell for many reasons, but they buy for exactly one (they think the stock is undervalued).
The strongest version of the signal is cluster buying: multiple officers and directors at the same company purchasing in the same window. A single CFO buy can be idiosyncratic; three officers buying in the same week is much harder to dismiss.
How InsiderWire surfaces Form 4 data
We pull Form 4 filings from OpenInsider (which mirrors EDGAR with cleaner formatting) every 5 minutes. Each P-coded purchase becomes a Signal row tagged source='sec_form4', with the insider's title, share count, and dollar value.
When three or more Form 4 purchases land on the same ticker within our consensus window, our scoring engine fires an insider-cluster event and (for Pro users) pushes a notification.
Keep reading.
Educational content. Not investment advice. InsiderWire aggregates publicly-available SEC and Congressional filings — past activity is not a guarantee of future returns.