When corporate insiders (officers, directors, and large shareholders) buy, sell, or otherwise transact in their company's securities, they must file a Form 4 with the SEC within two business days. Each transaction is tagged with a single-letter transaction code that describes the nature of the trade.
Understanding these codes is essential for interpreting insider activity. Not all insider transactions are equal — an open-market purchase (code P) carries a very different signal than an automatic tax withholding (code F).
Quick Reference Table
| Code | Transaction Type | Signal Strength | Description |
|---|---|---|---|
| Open Market Transactions | |||
| P | Open-market purchase | Strong bullish | Insider voluntarily buys shares on the open market using their own money. |
| S | Open-market sale | Moderate | Insider sells shares on the open market. Can be bearish, but insiders sell for many reasons. |
| Company-Related Transactions | |||
| A | Grant, award, or other acquisition | Weak / Routine | Insider receives shares from the company as compensation (stock awards, RSUs, bonus shares). |
| D | Disposition (sale back to company) | Weak / Routine | Insider sells or transfers shares back to the issuing company (e.g., share buyback). |
| F | Tax withholding | Routine | Company withholds shares to cover tax obligations when shares vest or options are exercised. Not a voluntary sale. |
| Derivative Transactions | |||
| M | Exercise/conversion of derivative | Weak / Routine | Insider exercises stock options or converts a derivative security into common stock. |
| C | Conversion of derivative | Weak | Conversion of a derivative security (e.g., convertible note to common stock). |
| X | Exercise of in-the-money derivative | Routine | Exercise of an in-the-money or at-the-money derivative security. |
| O | Exercise of out-of-money derivative | Weak | Exercise of an out-of-the-money derivative security. |
| E | Expiration (short position) | Informational | Expiration of a short derivative position. |
| H | Expiration (long position) | Informational | Expiration of a long derivative position. |
| Other Transactions | |||
| G | Gift | No signal | A bona fide gift of securities, either by or to the insider (e.g., charitable donation). |
| K | Equity swap | Moderate | Equity swap or similar hedging transaction. May indicate the insider is reducing risk exposure. |
| V | Voluntary report | Informational | A transaction voluntarily reported on Form 4 (not legally required to be reported). |
| J | Other | Varies | Other types of transactions described in footnotes. |
| I | Discretionary transaction | Weak | Discretionary transaction in an issuer plan. |
| L | Small acquisition | Weak | Small acquisition under Rule 16a-6. |
| U | Tender offer disposition | Moderate | Disposition pursuant to tender of shares in a change of control transaction. |
| W | Inheritance | No signal | Acquisition or disposition by will or the laws of descent and distribution. |
| Z | Voting trust | Informational | Deposit into or withdrawal from a voting trust. |
Most Important Codes for Investors
Code P - Open Market Purchase
This is widely considered the strongest bullish signal in insider trading analysis. When an insider spends their own money to buy shares on the open market, they are making a bet that the stock price will rise. Studies have shown that stocks with significant insider buying tend to outperform the market.
Code S - Open Market Sale
Insider sells are harder to interpret than buys. Insiders sell for many legitimate reasons: diversification, tax planning, personal expenses, pre-planned 10b5-1 trading plans, or estate planning. However, cluster selling (multiple insiders selling around the same time) or unusually large sales can be a warning sign.
Code M - Option Exercise
Option exercises are generally routine and tied to compensation packages. They often appear alongside code "S" transactions when insiders exercise options and immediately sell the shares ("exercise and sell"). The key distinction: watch whether the insider holds or sells the shares after exercising.
Code F - Tax Payment via Share Withholding
Code F transactions are not voluntary sales and should not be interpreted as bearish signals. When restricted stock units (RSUs) vest, the company withholds a portion of shares to cover the insider's tax liability. The insider has no discretion over this transaction.
How to Use Transaction Codes in Your Analysis
- Focus on P and S codes for directional signals. Other codes are mostly routine or administrative.
- Look at clusters — multiple insiders buying or selling around the same time is more meaningful than a single transaction.
- Consider the dollar amount — a $2 million purchase by a CEO is a stronger signal than a $10,000 purchase by a minor officer.
- Check the percentage — an insider increasing their position by 50% is more notable than a 1% increase.
- Filter out noise — ignore F (tax), A (grants), and M (exercises) unless the insider holds the shares.
Frequently Asked Questions
What is SEC Form 4?
Form 4 is a filing required by the SEC whenever a company insider (officer, director, or 10%+ shareholder) changes their ownership position in the company's securities. It must be filed within two business days of the transaction.
Is insider trading legal?
Yes, most insider trading is perfectly legal. Corporate insiders are allowed to buy and sell their company's stock, as long as they don't trade on material non-public information. All legal trades must be disclosed via Form 4 filings. It's only illegal when insiders trade based on confidential information not available to the public.
What is a 10b5-1 plan?
A 10b5-1 plan is a pre-arranged trading plan that allows insiders to set up automatic trades in advance. These plans provide a legal defense against insider trading accusations because the trades are predetermined. Sales under 10b5-1 plans are generally considered less meaningful as bearish signals.
Where does Insidersy get its data?
All data comes directly from SEC EDGAR, the SEC's Electronic Data Gathering, Analysis, and Retrieval system. We parse Form 4 XML filings as they are published and extract the transaction details for easy filtering and analysis.