By the InsiderAlpha research team · Updated Jul 16, 2026 · Sourced from SEC EDGAR filings
A cluster buy is when two or more corporate insiders at the same company purchase shares on the open market within a short window — typically 48 hours to 30 days. Cluster buying is one of the strongest and most consistently documented anomalies in insider-trading research.
A single insider purchase can be motivated by personal liquidity, a new-job share requirement, or simple optimism. But when several independent insiders — say a CEO, a CFO, and an outside director — all buy at roughly the same time, coincidence becomes an unconvincing explanation. The far more likely driver is that they are each responding to the same shared, asymmetric information about the company's near-term prospects: a turnaround taking hold, a contract about to close, or a valuation they collectively see as too cheap.
Cohen, Malloy & Pomorski (2012, "Decoding Inside Information") separated "opportunistic" insiders from "routine" ones and found opportunistic clustered buys generated value-weighted abnormal returns of roughly 8% per year. Lakonishok & Lee (2001) likewise found the predictive power of insider trading concentrates in active, multi-insider buying rather than isolated trades. Practitioner studies since have repeatedly confirmed that clusters outperform lone purchases.
Beware coordinated compensation events that look like clusters but aren't: a board-wide annual stock award, or several executives exercising options on the same vesting date. Pre-scheduled Rule 10b5-1 purchases that happen to overlap are also not genuine conviction clusters. We screen all of these out.
Our trading-plan generator adds a +15-point cluster bonus when two or more insiders purchase the same ticker within 48 hours, layered on top of role-weighted size and recency scoring. You can watch clusters form in real time on the live signal page.
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