Who is buying: how to read 13F and Form 4 filings without a subscription

Every officer, director and big shareholder of a US-listed company has to tell the SEC when they buy or sell their own stock. Every manager with more than $100 million in US stocks has to list what it holds, once a quarter. Both filings are free, on the SEC's website, the day they arrive. The subscription services selling "insider buying alerts" are reading the same two forms you can read tonight. Here is how I read them, on filings from the last three months.

Form 4: the two-day form

When an insider trades, a Form 4 goes to the SEC within two business days. An insider means an officer, a director, or anyone holding more than 10% of the shares. The form has the date, the number of shares, the price, and the holding afterwards. That is the whole thing, and it is the best of the three "who is buying" sources by a distance, because it is fast and it is specific.

Here is one I opened last night. On 17, 18 and 21 September 2026 Berkshire Hathaway bought 2,668,508 Class A shares of Lennar, the homebuilder, in eight lots at average prices per lot from $76.39 to $79.41, about $207 million, and filed the Form 4 on 21 September, the same day as the last lot. After the purchases it holds 23,719,109 shares. Berkshire files as a "10% owner"; Warren Buffett's name is on the form as well.

You could not have known any of that from the quarterly filing. Berkshire's 13F for 30 June, filed on 14 August, shows 13.1 million Lennar shares, up from 10.1 million in March and 7.1 million in December. Five weeks after that 13F arrived, the Form 4 put the holding at 23.7 million, nearly twice what the 13F had said. The Form 4 is the live feed. The 13F is the photograph from last quarter.

Two more from our filing table, because one example is an anecdote:

• Cascade Investment, the vehicle of Bill Gates, files as a 10% owner of Republic Services, the waste company. Between 10 August and 11 September 2026 it made 24 separate purchases at $215 to $225 a share, $871 million in all, each one on a Form 4 within two business days. Its holding afterwards: 117 million shares.
• Sumitomo Mitsui Financial Group bought 5,906,542 shares of Jefferies at $53.96 on 15 July 2026, $319 million, filed on 17 July. A strategic partner adding to a stake, which reads differently from a fund manager buying, and the form tells you which it is.

What Form 4 cannot tell you

Sells outnumber buys thirteen to one, and mean less. In our table, from 22 June to 21 September 2026, insiders filed 3,560 sales and 263 purchases. That is normal. Insiders are paid in stock, so they sell to pay tax, buy a house, diversify, or because a plan set a year ago said sell on that date. A buy has one reason: the buyer thinks the shares are worth more than the price. That asymmetry is why the buy list is short and worth reading and the sell list is long and mostly noise.

A corporate holder is not an insider with an opinion. Uber, which owns a stake in Aurora Innovation from the 2021 sale of its self-driving unit, sold 67.5 million shares in June, 72 million in August and 29.4 million in September, about $1.1 billion, all on Form 4. That is a company managing its balance sheet, not a verdict on Aurora, and the form looks identical to an officer selling. Read the filer's name before the direction.

The transaction code matters. A Form 4 marked P is an open-market purchase. A is an award (stock the company gave them, free). M is an option exercise. F is shares handed back to cover tax. Only P is somebody choosing to spend their own money. Screeners that count every Form 4 as "insider activity" are counting paydays.

Timing is two days, not zero. The median gap between trade and filing in our table is two days. The maximum in the last three months was 64. The form is fast; it is not instant, and the price has usually moved by the time you read it.

13F: the quarterly photograph

Any manager with more than $100 million in US equities files a 13F within 45 days of each quarter end, listing its long positions in US stocks above a small floor: name, share count, value at the quarter-end price. Berkshire, Citadel, BlackRock, Pershing Square, the lot. It is the source of every "what is Buffett buying" headline you have ever read.

Berkshire's for 30 June 2026, filed 14 August: Apple 22% of the listed portfolio, American Express 17%, Coca-Cola 11%, Bank of America 9% (cut by 6% in the quarter), Chevron 5%, and further down the Lennar line at 0.4%, up 30% in the quarter. That last line is the only one that would have told you something new, and it was already seven weeks old when it arrived.

What the 13F cannot tell you

It is late. Positions as of 30 June, public on 14 August. A share bought on 2 April is four and a half months old by the time you see it, and may have been sold since. Lennar above is the proof: the 13F said 13 million; the Form 4 of 21 September said 23.7 million.

It is long only. Shorts are not on it. Options appear as the underlying shares, which is why a market maker's 13F can show billions in a stock it has no view on at all. A hedge fund that is long a stock and short its rival shows you half the trade.

It does not tell you when inside the quarter. Two share counts a quarter apart; nothing in between. "Increased 30%" could be a steady build or a single Friday.

It only counts US stocks. No bonds, no foreign listings, no private holdings. For a manager with a large non-US book the 13F is a fragment.

Congress, for completeness

Members of the House and Senate disclose trades under the STOCK Act, with 45 days to file. In our table the House filings this year arrived a median 16 days after the trade, and the amounts are given as ranges, not figures. It is a pattern-over-months source, not a signal. If you want to know what a congressman owns, it works; if you want to know what to buy this week, it does not.

Reading them together: the routine

1. Start from the company, not the form. I open the insider list for a stock you already understand from its accounts. A buy on a company you have read means something; a buy on a company you have not is a tip in a filing.
2. Filter to P. Open-market purchases only; I do this before reading a single name. Then look at the size against the buyer's existing holding: a director doubling a $200,000 stake is a bigger statement than a founder adding 0.1%.
3. Read the filer's name. Officer, director, fund, corporate holder, or a 10% owner topping up. Each is a different sentence.
4. Use the 13F for the shape, not the timing. Which managers own it, how concentrated they are, whether the count rose or fell. Then go back to the Form 4s for what has happened since.
5. Write it beside the fundamentals, not instead of them. Berkshire buying Lennar tells you a careful buyer likes the price; the 10-K tells you what the price is buying. Neither works alone.

Our Smart Money page keeps the three sources in one place with the date on every row, so you always know how old a trade is; its documentation describes what is and is not in it. The insider list is on every company page, and the one-company report includes it. Reading the forms yourself on the SEC's site costs nothing and takes ten minutes once you know the codes. That is the whole trick the alert services are selling.

Educational and proprietary. This explains what our research does, not the exact formula behind it, and it is not personalised investment advice. See the full disclaimer.