What Is a 13F: How to Read Famous Investors' Portfolios

Every institution in the US that manages more than $100 million in stocks must report its holdings to the SEC at the end of each quarter. That report is the 13F. Every headline about what Berkshire Hathaway, Pershing Square or Bridgewater "bought" comes from this document.

What It Shows

A 13F line tells you three things: which company, how many shares, and their value at the quarter-end price. Put two consecutive filings from the same manager side by side and the buying and selling appear:

• New: a position that was not there last quarter.
• Added / Trimmed: a position whose share count changed.
• Sold Out: a position that was there last quarter and is gone now.

The comparison uses SHARE COUNTS, not dollar values. If a stock rises 30%, its value rises 30% too; the manager may not have bought a single share.

What It Doesn't Show

Option Lines Can Mislead

Calls and puts appear in a 13F too. But the value on that line is not the premium paid for the option; it is the value of the UNDERLYING shares. A "$10 billion put" headline does not mean the fund paid $10 billion; it is the quarter-end value of the shares the options cover. Opening Bell shows these lines separately from the stock portfolio and leaves them out of the weights.

Why Copying Is Risky

Buying what a famous investor bought looks like a tempting shortcut. It has three problems:

• 01You are late. By the time you see it, the trade happened weeks, often months, ago. The price may already have moved.
• 02You don't see the whole. The position may be part of a hedge or another asset you cannot see.
• 03Their scale is not yours. A 1% experiment in a portfolio of hundreds of billions could be your entire savings.

A 13F is a source of ideas, not a buy signal. Trying to understand why an investor believes in a company teaches far more than copying what they bought.

Congressional Disclosures

Members of the US Congress and their spouses must report stock trades above $1,000 within 45 days under the STOCK Act. These reports differ from a 13F in two ways:

Because the amount is only reported as a range, the true size of a trade is unknown; reading the middle of the range as a single number would be invented precision.