Does the size of an insider buy matter?

It is tempting to weight a $5 million insider purchase far more heavily than a $50,000 one. We tested whether dollar size actually predicted better returns: across 45,712 open-market buys over five years, we split purchases into size buckets and measured the next 30, 60 and 90 days against the Russell 2000.

Bigger buys did not mean bigger returns

The three size buckets barely differed, and the trend ran the wrong way: the largest purchases underperformed the smaller ones on both win rate and average return. A giant buy is often a founder or 10% holder adding to an already-huge position, which carries less signal than a first, deliberate purchase by an executive.

The edge is early

As in every slice of this data, the advantage is strongest in the first 30 to 90 days and fades after that. Insider buying reads like a short-to-medium-term catalyst, not a set-and-forget signal, which is why we track it live and mark every buy on the price chart.

Methodology & caveats

We start from every open-market purchase (SEC Form 4, code P) of $10K or more filed over the last five years across the US market, enter at the closing price on or just after the transaction date, and measure the return 30, 60 and 90 days later against the Russell 2000 over the same dates. "Cluster" means that many different insiders bought the same company within 30 days. Option exercises, grants, and obvious price-data errors are excluded, as are tickers with no daily price history. Returns shown are averages (means); because a few big winners can lift an average, we also show how often each signal was simply positive and how often it beat the market. Buckets are by the reported dollar value of the individual purchase. Caveats: this covers 2021-2026 only, one bull market plus the 2022 selloff, not a full range of cycles. This is analysis of past filings, not a prediction or investment advice. Past performance does not predict future results.