Insider Buying vs Insider Selling: Which One Matters?

Most executives are paid largely in stock. They are already overexposed to their employer, so selling some is the sensible default. Buying more, on the open market, goes against that default. That asymmetry is why decades of research treats insider purchases as the informative side of the ledger.

• →A cluster: three or more insiders selling inside a short window.
• →A large share of holdings: an officer selling most of their stake, not a slice.
• →Timing: a sale that is not under a 10b5-1 plan, shortly before a known event.

InsiderWatch does not alert on single sales. It tracks every significant non-plan sale in a rolling 30-day log and alerts only when a cluster forms at one company.

A company with steady insider buying and no selling is the pattern worth noticing. A company with one buy and many sales is not. Look at the direction of the whole group over a month, not one filing.

A large share of what is reported as insider selling never involved a decision to sell. Restricted stock units vest on a schedule, and on the vesting date the company withholds a slice of the shares to cover tax; that shows on a Form 4 as a code F disposition. Options are exercised and the shares sold the same day to fund the exercise, a code M followed by a code S. Sales under a 10b5-1 plan run on a calendar fixed months earlier. None of these tells you what the insider thinks of the stock today.

Then there are the discretionary sales that still carry little information: diversification for an executive whose net worth is mostly one stock, a house purchase, estate planning, a divorce, an ownership guideline already met many times over. The seller usually has to disclose nothing about the reason, so a reader cannot separate these from a sale made on a view.

An open-market purchase has only one explanation that survives scrutiny: the buyer expects the shares to be worth more. There is no vesting schedule that makes an executive buy, no tax bill that is paid by buying, and no diversification argument for adding to a position that already dominates their wealth. Some purchases are still made for show, a small buy after a bad quarter to steady the stock, and those are usually visible by their size: a token amount against the buyer's pay and holdings.

This is why the research literature going back decades finds that insider purchases predict returns on average and insider sales barely do, and why the effect is strongest for senior officers, for clusters of buyers, and in smaller companies. It is also why InsiderWatch alerts on buys and treats sales as context.

• →The share of holdings sold. An officer selling 5% of their stake is trimming; one selling 60% is leaving. The "amount owned following" column on the Form 4 gives the denominator.
• →The plan checkbox. A sale outside any 10b5-1 plan was a decision made now.
• →Timing against known events. A discretionary sale in the weeks before an earnings report or a product decision is the kind that has drawn enforcement attention, and it is rare for that reason.
• →Company. Several insiders selling discretionary blocks in the same window, at a company that has just run up, reads differently from one executive's annual diversification sale.

A useful single number is net open-market activity over 30 days: dollars bought by insiders with their own money minus dollars sold outside plans. A company where that number is positive after a fall is the pattern insider-buying strategies look for. A company where it is large and negative after a rise is worth caution, though it is weaker evidence in the other direction. The live counts below show the two sides for the whole market over the recent window.