Insider Transactions: How to Read a Form 4

Executives' trades in their own company's stock are public; why sales say much less than purchases.

A company's executives can buy and sell their own company's stock; that is legal. What makes it legal is that the trade is disclosed to everyone. In the US that disclosure is called a Form 4, and it has to be filed with the SEC within two business days. Headlines like "CEO sells millions of dollars of stock" usually come from this form, and the form itself tells you more than the headline.

Transaction Codes

The most important column on a Form 4 is the transaction code. The same "decrease in shares" says very different things depending on its code.

Code	Meaning	What It Says
P	Open market or private purchase	The executive bought with their own money; the strongest signal
S	Open market or private sale	Says little on its own; there can be many reasons
M	Exercise or conversion of an option or derivative	Part of the pay package
A	Grant or award from the company	Like salary; not a decision
F	Shares withheld for tax or exercise price	Automatic; carries no information
G	Gift	Usually tax planning
X	Exercise of an in-the-money option	Similar to M

Why Sales Are Noisy

A large part of executive pay comes as stock and options. So they have many reasons to sell: paying taxes, buying a house, diversifying their wealth away from a single company, or following a sales plan set up years ago. None of these is a view on the company's future.

Buying, in practice, has just one reason:

Insiders might sell their shares for any number of reasons, but they buy them for only one: they think the price will rise.

The line is attributed to Peter Lynch, and it sums up the main rule of reading a Form 4: open-market purchases with the insider's own money (P) are rare and informative; sales are frequent and mostly noise.

Planned Sales

10b5-1 plans are programs an executive sets up when they have no inside information and can't interfere with afterward. Since 2023, officers must wait at least 90 days between adopting a plan and the first trade, and the Form 4 has a box showing whether a trade was made under a plan. A planned sale carries no signal about timing; when the plan was adopted or cancelled, however, can.

Patterns That Can Matter

Cluster buying. Several executives buying in the open market in the same period is a stronger sign than a single purchase.
Buying after a drop. An executive buying with their own money after a sharp decline can show they think the price has fallen too far relative to the inside view.
Large sales outside a plan. Sales without the 10b5-1 box checked, far above the usual size and from several executives, are worth a closer look.

None of these alone is a reason to buy or sell. Executives get things wrong too, and their purchases are often proven right only months or even years later.

Where You'll See It on This Site

This site doesn't list insider transactions. You can find a company's Form 4 filings by searching its name in the SEC's EDGAR database and filtering by form type. A company buying back its own shares is a separate topic: What Is a Share Buyback?

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