Insider transaction codes: which Form 4 filings carry signal
An executive selling ten million dollars of stock usually means nothing at all. Reading Form 4 filings well is mostly a matter of throwing most of them away.
Company insiders report their transactions on Form 4 within two business days. The filings are public and free. They are also mostly noise, because most of what an executive does with company stock is not a decision about the company at all.
The codes
| Code | What it is | Signal |
|---|---|---|
| P | Open-market purchase | Real. The insider spent their own money |
| S | Open-market sale | Real, but weaker. See below |
| M | Option or derivative exercise | None. A compensation event |
| F | Shares withheld to cover tax | None. Mechanical |
| A | Grant or award | None. Compensation |
| G | Gift | None |
| C, J, X | Conversion and other | None in practice |
The practical consequence is severe. One Apple filing shows thirty thousand shares acquired under code M and sixteen thousand disposed under code F on the same day. A tracker that ignores codes reads that as a thirty thousand share purchase and a sixteen thousand share sale. Neither happened. An option vested and tax was withheld.
10b5-1 plans
A sale executed under a Rule 10b5-1 plan is a calendar carrying out an instruction given months earlier, usually before the insider knew anything about the current quarter. The filing carries a flag for it. Such a sale should be set aside entirely rather than scored as a small negative, because averaging a zero into a score still drags the score.
Why dollar totals mislead
One hundred and eight million dollars of insider selling sounds alarming until you note the company is worth four and a half trillion. That is roughly a quarter of a basis point of the market capitalisation. Any measure of insider activity has to be relative to company size or it will simply rank the largest companies as the most bearish.
Buying and selling also deserve different scales. Insiders are paid in stock and have to sell some of it to diversify or to buy a house. Buying costs them cash they could have spent on anything. A sale should have to be roughly an order of magnitude larger than a purchase to carry the same weight.
Silence is neutral
Across twenty-five recent Form 4 filings each for two large companies, the number of open-market purchases was zero. Large-cap insiders rarely buy. If no activity reads as bearish, every mega-cap is permanently bearish and the measure is useless. Absence of activity is a neutral reading.
One thing that is not neutral: a failed data fetch. A tracker that cannot reach the filings and a company whose insiders did nothing look identical unless the system distinguishes them explicitly. If a platform ever tells you an insider signal is neutral, it is worth knowing whether it actually read anything.
Run this on a company you know
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