How do you read insider buying, and when does it matter?

By Daniel, The Philosopher Investor · updated October 2, 2026

Who counts as an insider, and what do they file?

Section 16 of the Securities Exchange Act covers a company's officers, its directors and anyone holding more than ten percent of a class of stock. Every time one of them buys or sells the company's shares they file a Form 4 with the SEC, due by the end of the second business day after the trade. The filing shows the date, the number of shares, the price, and the holdings after the trade.

Form 4s are public the moment they are filed, on EDGAR, and trackers read them within minutes. Unlike Congress disclosures the lag is short, so the data is close to current. The volume is large: thousands of filings a week across the US market, most of them routine.

Which purchases carry information?

Open-market purchases with the insider's own cash. The Form 4 transaction code is P for these. Everything else is weaker: option exercises, restricted stock vesting, shares received under a plan, purchases through a dividend reinvestment. Those are compensation mechanics, and they happen on a schedule regardless of what the insider thinks.

Size relative to the insider's existing position is the second filter. A CEO who owns two million shares buying five thousand is making a gesture. A director who owns twenty thousand buying twenty thousand has doubled down. The dollar figure alone misleads because insiders' wealth varies so much.

Why do sales say so little?

Insiders sell to diversify, to pay taxes on vested stock, to buy a house, to fund a divorce, or because a pre-arranged 10b5-1 plan sold on schedule. Only one of the many reasons to sell is a negative view of the company. Studies of insider transactions consistently find that purchases predict returns and sales, in aggregate, do not.

The exception is a sale that breaks pattern. An insider who has never sold, selling a large share of holdings outside any plan, shortly after a run-up, is worth a look. Even then it is a question rather than a signal.

What is a cluster buy?

Three or more insiders buying on the open market within a short window, typically a few weeks. It is the single pattern in insider data with the most consistent record. One insider can be wrong or be making a gesture. Several insiders, each with their own view of the business, each spending their own money, agreeing at the same time is a different thing.

Clusters after a decline are the strongest form. The stock has fallen, the people who know the business best are buying, and they are doing it together. The trade that follows is still a trade, with all the usual risks, but the odds have shifted.

How do you use it?

As a screen and a confirmation, never as a trigger. A cluster buy puts a name on the list. The chart then has to make sense, and the reason for the decline has to be one the insiders could plausibly see through. Insiders are early, often by months, and a stock can keep falling after they buy.

Watch the same names for follow-through. An insider who bought in March and buys again in June, at a lower price, is telling you something twice. Repeated purchases by the same person over a year is the slow, patient version of the cluster, and it has a similar record.

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