An unusually large insider buy is a single SEC Form 4 open-market purchase at least 2x that same insider's own historical median buy: large relative to their own history, not just a big absolute dollar number.
Company insiders operate at wildly different personal scales — a CEO and a junior director can differ by orders of magnitude in what a "normal" purchase looks like for them. Comparing every buy to one fixed dollar line would drown out small-scale insiders and treat routine buying by large-scale ones as remarkable. Normalising each buy to that insider's own median surfaces a genuine change in an individual’s behavior, not just who has the biggest wallet.
Concretely, Quantustik divides this buy’s dollar value by that insider's median past buy value, and flags the row when that ratio is 2.0 or higher. The ratio is only defined for purchases — sells are never flagged — and an insider with no prior buys on record is left unflagged rather than guessed at.
Example (illustrative): if a director’s past open-market buys have a median size of $40,000 and they file a new $120,000 purchase, the ratio is 3.0 — above the 2.0 threshold — so the row is tagged "Unusually large." These figures are illustrative, not a live reading.
Quantustik divides the buy's dollar value by that same insider's median past buy value; a ratio of 2.0 or higher (at least twice their own typical size) gets the flag. It is computed only for purchases, never for sells.
Insiders operate at very different personal scales. Normalising to each person's own median surfaces a real change in their behavior, not just who has the biggest wallet.
Browse all S&P 500 tickers to see this metric applied to individual companies.
Educational research only — not investment advice.