What is a Form 4 Filing? Definition, Formula, and Example
A Form 4 is the SEC filing corporate insiders must submit within two business days of buying, selling, or receiving their own company's stock, making every insider transaction public almost in real time.
What Is a Form 4 Filing?
Form 4 is an SEC-mandated disclosure that officers, directors, and beneficial owners of more than 10% of a company's stock ("Section 16 insiders") must file every time they transact in their own company's securities. It covers open-market buys and sells, option exercises, restricted stock vesting, gifts, and 10b5-1 plan trades. Unlike quarterly filings, Form 4 has a hard two-business-day deadline from the transaction date, which makes it the fastest public window into what the people running a company are actually doing with their own stock — as opposed to what they say on earnings calls.
How It's Identified and What It Contains
Every Form 4 breaks a transaction into structured fields:
- Table I — non-derivative securities (common stock bought/sold outright)
- Table II — derivative securities (options, RSUs, warrants)
- Transaction code — the single most important field for reading intent:
- P = open-market purchase (highest-conviction signal)
- S = open-market sale
- A = grant or award (routine compensation, not a market decision)
- M = option exercise
- F = shares withheld to cover tax on vesting (automatic, not discretionary)
- G = gift
- Shares transacted, price, and post-transaction ownership — lets you compute exactly what percentage of an insider's stake changed hands.
The filing is submitted electronically via SEC EDGAR and is publicly searchable within hours.
Worked Example: Commercial Metals (CMC)
On July 13, 2026, CMC President and CEO Peter R. Matt filed a Form 4 reporting a direct open-market purchase of 8,230 shares at a weighted average price of $61.30, a transaction coded P — a discretionary buy, not a grant or tax-withholding event. The trade totals roughly $504,600. Because it's a code-P purchase by the sitting CEO rather than a scheduled 10b5-1 sale or option-related transaction, it reads as a genuine conviction signal: the filing tells the market the CEO chose, out of his own after-tax cash, to add to his position at the prevailing market price.
When Traders Use Form 4 Data
Retail and quant screens alike track Form 4 filings for cluster buying — multiple insiders (not just the CEO) purchasing stock within a short window, which historically correlates with modestly better forward returns than single, isolated buys. Screeners like OpenInsider, GuruFocus, and Tapeboard's insider-flow panel filter specifically for code-P transactions and exclude routine A/F/M entries, since those are compensation mechanics rather than market bets. Sudden insider buying after a stock has sold off sharply is a common setup traders watch for as a contrarian signal, especially when it comes from a CEO or CFO rather than a lower-ranked officer.
Limitations and Common Misconceptions
Insider *selling* is a far weaker signal than insider *buying* — executives sell for diversification, tax planning, real estate purchases, or divorce settlements that have nothing to do with their view on the stock, and a huge share of sales are pre-scheduled 10b5-1 plan trades set up months in advance. The two-business-day filing window also means the price you see may already be stale relative to where the stock trades by the time the filing hits EDGAR, especially around volatile news. And a single Form 4 purchase, however well-timed historically, is not proof of superior insider information — it's a probabilistic tilt, not a guarantee, and should be read alongside fundamentals, not as a standalone buy signal.