What Is a Cluster Buy? When Several Insiders Buy at Once
A cluster buy is when two or more different insiders of the same company buy its stock on the open market within a short period of each other. It is not an SEC term but a way investors group Form 4 filings. On InsiderHound, a cluster buy means at least two insiders buying (Form 4 code P) within 7 calendar days, by trade date.
Key takeaways
- A cluster buy combines several separate Form 4 purchases by different insiders of one company.
- Investors watch them because several people with inside knowledge chose to put their own money in at about the same time.
- Check the code (P only), the size against each insider’s holdings, and who is buying.
- A cluster buy is a data point, not a prediction. The stock can still fall.
Why investors pay attention
Insiders sell for many reasons — taxes, diversification, a house — but there is usually one main reason to buy: they expect the shares to be worth more. When several insiders buy within days of each other, it is less likely to be one person’s personal situation. Academic research, such as Lakonishok and Lee (2001), has found that insider purchases have on average carried more information about future returns than insider sales, while also showing that the effect varies widely between companies.
What to check in a cluster buy
- The code is P. Grants (A), option exercises (M) and tax withholdings (F) do not count. See Form 4 transaction codes.
- Who is buying. A CEO or CFO buying is different from a fund that owns more than 10% adding to a stake.
- The size. Compare each purchase with the insider’s holdings after it. Adding 50% to a stake says more than adding 1%.
- The timing. Purchases right after a large price drop or right after an earnings report are common, because company trading windows open then.
- The dates. Make sure the purchases are recent by trade date, not only by filing date. Some filings arrive late.
An example of how a cluster is counted
| Insider | Code | Trade date | Value | In the cluster? |
|---|---|---|---|---|
| Director A | P | Monday | $150,000 | Yes |
| CFO | P | Thursday | $80,000 | Yes |
| CEO | M | Friday | — | No: option exercise, not a purchase |
Swipe the table to see all columns.
The cluster here is two insiders and $230,000 of purchases. The CEO’s option exercise is reported on the same days but is not part of it.
The limits of cluster buys
- Insiders can be wrong, and a stock that insiders buy can keep falling.
- Some clusters are coordinated on purpose to show confidence after bad news.
- Small companies can show large percentage changes from small amounts of money.
- Form 4 does not say why someone bought.
Sources: SEC Form 4 General Instructions; Josef Lakonishok and Inmoo Lee, “Are Insider Trades Informative?”, Review of Financial Studies 14, no. 1 (2001) (accessed November 9, 2026). Educational content, not investment advice.