Form 4 Transaction Codes Explained: P, S, A, M, and More

Every transaction reported on SEC Form 4 includes a single-letter transaction code that identifies the nature of the trade. These codes tell you whether an insider bought shares on the open market, received a stock option grant, exercised existing options, or made a gift of securities — and the distinction matters enormously when interpreting insider activity.

Not all insider transactions carry equal weight as investment signals. Understanding what each code means allows you to filter out routine administrative transactions and focus on the ones that genuinely reflect insider sentiment.

Open Market Transactions: P and S

The two most important transaction codes for investors are the simplest to understand.

P — Open Market Purchase. The insider bought shares on the open market using their own money at the prevailing market price. This is the strongest form of insider conviction. When a CEO writes a personal check to buy company stock at the same price available to any public investor, it signals genuine confidence in the company's future. You can track these on InsiderFlow's insider buying page.

S — Open Market Sale. The insider sold shares on the open market. Sales require more nuance to interpret. Insiders sell for many reasons — taxes, diversification, home purchases, estate planning — so a single sale is not necessarily bearish. However, heavy selling by multiple insiders or selling that deviates from historical patterns can be meaningful. Browse current activity on the insider selling page.

Compensation-Related Codes: A, M, F, and C

A large portion of Form 4 filings relate to compensation rather than voluntary market transactions. These codes represent transactions that are typically part of pre-arranged compensation programs.

A — Award or Grant. The insider received securities as part of their compensation package. Stock option grants, restricted stock unit (RSU) awards, and performance share grants all use this code. Because the insider did not choose to buy at the current price, A transactions are generally not considered a signal of the insider's view on valuation. However, they do show how much of the insider's compensation is tied to equity performance.

M — Option Exercise or Conversion. The insider exercised a previously granted stock option or converted a derivative security into common stock. An M transaction in Table II of the Form 4 is often paired with additional transactions in Table I — either a holding of the newly acquired shares or an immediate sale (coded S). The key question is what happens after the exercise: holding suggests confidence, while an immediate sale is more neutral.

F — Payment of Exercise Price or Tax Liability. This code indicates shares were withheld or surrendered to cover the tax obligation triggered by a vesting event or option exercise. F transactions are almost entirely mechanical — the insider is not making a discretionary decision to sell. The company withholds just enough shares to satisfy the tax bill. These are among the least informative transactions on Form 4 and can typically be filtered out when analyzing insider sentiment.

C — Conversion of Derivative Security. Similar to M, this code is used when a derivative security is converted into another form, though it specifically applies to conversions of instruments like convertible notes or convertible preferred stock rather than traditional option exercises.

Transfer Codes: G, W, and J

Several transaction codes capture transfers that do not involve a purchase or sale on the open market.

G — Gift. The insider gifted shares to another party, such as a family member, trust, or charitable organization. Gifts do not involve a cash transaction, so no price is reported. While large gifts can reduce an insider's direct holdings, they typically reflect estate planning or philanthropic activity rather than a negative outlook on the stock.

W — Acquisition or Disposition by Will or Laws of Descent. This code is used when shares are transferred as part of an inheritance, either acquired from a deceased person's estate or distributed from an estate. These transactions are entirely non-discretionary and carry no informational value about company prospects.

J — Other Acquisition or Disposition. This is a catch-all code for transactions that do not fit neatly into other categories. Examples include transactions resulting from mergers, stock splits, or other corporate actions. When you see a J code, the footnotes section of the Form 4 will typically explain the specific circumstances.

Disposition to Issuer: D

D — Disposition (Sale) to the Issuer. The insider returned or sold shares back to the company itself, rather than selling on the open market. This can occur during share buyback programs where the company repurchases stock directly from insiders, or when restricted stock is forfeited back to the company due to failure to meet vesting conditions. Like F transactions, D codes are often mechanical rather than discretionary.

Which Transaction Codes Matter Most for Investors?

If you are using insider trading data to inform investment decisions, the hierarchy of informational value looks like this:

• Most informative: P (Purchase) and S (Sale). These are voluntary, discretionary transactions where the insider is choosing to use their own capital. Open market purchases, in particular, have been shown in academic research to have predictive value for future stock returns.
• Moderately informative: M (Option Exercise). The decision of what to do after exercising — hold or sell — provides some signal, but the exercise itself is often driven by expiration timing rather than conviction.
• Least informative: A (Award), F (Tax), G (Gift), W (Inheritance), D (Disposition to issuer). These transactions are either non-discretionary, compensation-related, or administrative. While they affect the insider's total holdings, they say little about the insider's view of the stock's value.

Filtering for Meaningful Transactions on InsiderFlow

InsiderFlow automatically categorizes Form 4 filings by transaction code, making it easy to focus on the trades that matter. The insider buying page shows only open market purchases (code P), filtering out the noise of option exercises, tax withholdings, and grants that dominate raw Form 4 data.

For an even more focused view, the CEO purchases page narrows results to open market buys by chief executive officers — the insiders with the deepest operational knowledge of their companies. And the cluster buys page highlights cases where multiple insiders at the same company are buying within a concentrated period, which academic research suggests is an even stronger indicator than individual purchases.

Understanding transaction codes transforms raw Form 4 data from an overwhelming stream of filings into a curated set of meaningful insider signals. For a broader understanding of how these codes fit into the overall Form 4 structure, see our step-by-step guide to reading Form 4.