What is Form 4?
Form 4 is a filing that company insiders — officers, directors, and holders of more than 10% of a company's stock — are legally required to submit to the SEC whenever they buy or sell shares (or receive/exercise options, RSUs, and other equity awards) in the company they're affiliated with. It's filed under Section 16 of the Securities Exchange Act of 1934.
Each Form 4 is public and free to access on EDGAR, the SEC's electronic filing system. That's the entire premise of InsiderTradingRadar: the data is already public, the value is in catching it the moment it's filed, parsing it correctly, and filtering out the transactions that aren't a real trading decision.
What's on a Form 4
A Form 4 discloses the reporting person's relationship to the company (officer, director, or 10% owner, plus title), the transaction date, a transaction code describing what kind of transaction it was, the number of shares, the price per share, whether shares were acquired or disposed, and the person's resulting total ownership. Filings are split into Table I (common stock and other non-derivative securities) and Table II (options, RSUs, warrants, and other derivative securities) -- some tools only parse Table I and silently miss derivative activity.
Why the transaction code matters
Not every Form 4 reflects a discretionary decision. A code "P" (open market purchase) is a genuine buy decision. A code "A" (grant/award) or "F" (tax withholding on a vested award) is mechanical compensation activity that happens on a schedule, regardless of what the insider thinks about the stock. Treating every Form 4 as a signal, without distinguishing these, is the single most common way insider-trading tools produce noise instead of signal. See Form 4 transaction codes explained for the full code table.
When Form 4 is due
Form 4 is legally due within two business days of the transaction. Late filings happen, and amendments (Form 4/A) are filed when an original filing needs correction.
Form 4 vs. Form 3 and Form 5
Form 3 is an insider's initial ownership statement, filed once when they first become an officer, director, or 10% owner. Form 5 is an annual statement covering any transactions that were eligible for delayed reporting during the year. Form 4 -- ongoing, transaction-level disclosure -- is the one that matters for real-time alerting, and it's what InsiderTradingRadar tracks.