Insider buying: what it is and this month's S&P 500 buys

It is the filing through which the people with privileged access to a US company — its directors, its officers and any shareholder owning more than 10% — tell the SEC, the US securities regulator, that they have moved shares of that company. It is due within two business days of the trade, and it is public: anyone can read it on EDGAR, the SEC's document database.

It has two tables. The first covers shares: purchases, sales, deliveries. The second covers derivatives: options, restricted stock units. This site publishes the first in full and leaves out the second, because its price is the exercise price, not the market price; when an exercise delivers shares, it already shows up in the first table.

A director receives shares as pay (A), hands some back to cover the tax on those same shares (F), exercises options (M), and sells for a thousand reasons that say nothing about the company: diversifying, buying a house, paying another tax bill. Buying is the only thing on that list that costs them their own money, and that is why it is rare: 993 of 42,295 lines, 2.3%.

In dollars too. Over the same period, open-market sales add up to about $71,853 million and purchases to about $4,308 million. And nearly a quarter of the purchases is a single one: Elon Musk's in Tesla, $1,000 million on September 12, 2025.

Many sales are not this week's decision. Under a 10b5-1 plan, the insider writes down in advance — at a time when they hold no inside information, and with a mandatory waiting period — when and how much they will sell; the plan then runs on its own. Form 4 carries a checkbox saying whether the trade was made under such a plan, and this site reads it and shows it on every row.

In the history, 5,173 of the 9,067 sales have that box ticked, 57%. In September, 300 of 460, 65%. A pre-planned sale is still information, but it does not say the same as one decided yesterday. Nor are all purchases spontaneous: 64 of the 993 have the box ticked.

• One share a day. Horizon Kinetics, a more-than-10% holder of Texas Pacific Land (TPL), reported 12 purchases of a single share each, worth about $350-380 apiece.
• Dividend reinvestment and employee plans. A TPL director ($1,858), a PPG officer ($1,409) and a Consolidated Edison officer ($111): the footnotes say these are automatic dividend reinvestment or employee stock purchase plan buys.
• Late filings. A Stryker (SYK) director filed on September 2 five purchases made between 2019 and 2022, of between $557 and $12,739.
• Money changing pockets. Lachlan Murdoch, executive chair and CEO of Fox (FOXA), reported a purchase of 149,934 shares for $10.27 million. The same form shows the sale of those same shares: according to the footnote, he sold them to his family trust. No new money went in.

The first thing that stands out is that a single buyer outweighs all the others combined: Cascade Investment, which files the form together with William H. Gates III, adds up to $695 million in Republic Services, 94.6% of all the money spent on purchases this month. It bought in each of the ten sessions from August 28 to September 11, and after the last one it reports 117,058,444 shares. A streak like that is one decision repeated, not ten signals.

The second: at Uber, the chief operating officer (on September 4) and the chief executive (on the 10th) both bought, $15.3 million between them; and at Cooper Companies, three different directors bought between September 11 and 16. Several people at the same company buying around the same time is a different fact from a single buyer, and the site lets you see it company by company.

For context: over the same days, 460 open-market sales were reported at 165 companies, for about $2,545 million.

It is the obvious question, and the honest answer is that, with the data we have, it cannot be decided. We measured it over 709 purchase alerts at 198 companies between August 2025 and August 2026:

• Insiders buy after declines. Over the three months before the alert, the stock was on average 6.03% behind the equal-weight S&P 500 (median, 9.78%).
• The reaction comes overnight. From the close of the day the form is published to the next open, the stock rises 0.36% on average; from that open to the close, 0.19%. Most of the move happens before anyone can buy.
• At one month, positive and not significant. After removing what the multi-factor score already explains, companies with a purchase beat the rest by 0.561% per 21-session period, with a 95% confidence interval from −0.175% to +1.297%. Zero is inside it.

Thirteen months is far too little to separate a signal this size from noise. We are not saying purchases mean nothing; we are saying that, with this history, it is not proven that they mean anything usable, and that anyone who reads a purchase as a signal does so without that proof.

• The code. P is a purchase; S, a sale. Everything else is pay, tax, options or gifts.
• The 10b5-1 box. If it is ticked, the trade was decided months earlier.
• Who. A director, an officer and a fund with more than 10% do not know the same things or buy for the same reasons.
• Size against what they already hold. The form says how many shares they own afterwards; $100,000 does not weigh the same for everyone.
• The footnotes. That is where you read whether it was dividend reinvestment, an employee plan or a transfer to a trust.
• The two dates. The trade date and the filing date. Nobody could know before the second.

• Only the S&P 500 and only Table I. Options and restricted stock from Table II are not included.
• Names are not normalized. The SEC receives them as free text and the same person can appear spelled two ways; to group by person, the CSV includes the filer's identifier.
• A row is a decision, not an execution. When a broker splits an order into many fills, the site merges them into one row at the average price.
• The last day is always incomplete. The count is by filing date and there are two business days to file: September's figures will change as the remaining forms arrive.

Purchases, updated daily and with the SEC filing linked on every row, are on Insider Buying. Every transaction, with filters by code, relationship, amount and 10b5-1 plan, is on Insider Alerts, and each company has its own page (for example, Uber's). Everything downloads as CSV, no account needed: the purchase history. With a free account you can switch on an email alert for the day an insider reports a purchase above $250,000.