What Is a 13F Filing?
A 13F is a report that large institutional investment managers in the United States must file with the Securities and Exchange Commission every three months, listing the US-listed shares they held at the end of the quarter. It is the reason anyone outside Berkshire Hathaway knows what Warren Buffett owns, and the source behind every "here's what the great investors are buying" article you have ever read.
It is genuinely useful. It is also misunderstood more often than almost any document in public markets, mostly because of what it leaves out.
Who has to file one
The requirement applies to institutional investment managers who exercise investment discretion over $100 million or more in what the rules call Section 13(f) securities. That covers hedge funds, asset managers, banks, insurers, pension funds and some corporations.
Filings are due within 45 days of the end of each calendar quarter, and they are public on the SEC's EDGAR database as soon as they land.
What the filing actually contains
Less than most people assume. Each position on the form carries:
the name and class of the security
its CUSIP identification number
the number of shares held at the close of the quarter
the total market value of that holding
That is the list. There is no commentary, no reasoning, no cost basis, and no indication of what the manager intends to do next.
What a 13F does not show you
This is the part worth reading twice, because almost every mistake people make with 13F data comes from one of these gaps.
The data is up to 45 days old before you see it. A filing published in mid-February describes positions held on 31 December. A manager can buy in October, file in February, and have sold in January — and the filing will still show the position. You are looking at a photograph, not a live feed.
Short positions are not reported. Only long holdings appear. A fund showing a large position in a company may be hedging it with a short somewhere else, or holding it against an offsetting bet the form never reveals. The published list can be the opposite of the real exposure.
Whole asset classes are missing. Bonds, cash, commodities, currencies, private companies and most derivatives fall outside Section 13(f). So do shares listed outside the United States. A manager with most of their capital in Japanese equities or corporate credit will show a 13F that represents a fraction of what they actually run.
Anything bought and sold inside the quarter is invisible. Only the closing snapshot is reported, so a position opened in January and closed in March never appears at all.
Position size is not conviction. A $200 million holding sounds enormous until you learn it is under 1% of the fund. Without knowing the size of the whole portfolio, and how much of it is reportable, the dollar figure tells you very little about how much the manager cares.
Not every filer is picking stocks. Index funds and passive managers cross the threshold too. Their holdings reflect a benchmark, not a view.
You never learn the price paid. Following someone into a position they built far lower means taking the same idea with none of the cushion — and without the reasoning that would tell you when they'd change their mind.
The core problem with copying: you can see the what, never the why. If you buy a company because a well-known investor owns it, you have no framework for what to do when it falls 30%, because you never had a thesis of your own to test. The filings tell you nothing about when they intend to sell, and by the time the next one arrives, they may already have.
How to actually use 13F data
Treat it as a source of ideas rather than a list of recommendations. That single shift makes the whole exercise worthwhile.
The most useful patterns show up over time rather than in any one filing. A manager adding to the same position across four consecutive quarters is saying something that a single appearance does not. So is a position held patiently through a year in which the share price fell.
Overlap is the other signal worth noticing. When several managers with genuinely different styles — a concentrated value investor, a quality-focused manager, an activist — independently hold the same business, it is usually worth understanding why, even if the answer turns out to be no.
Then do the work yourself. Read the filings, look at ten years of the numbers, form a view on what the business is worth, and decide at what price it interests you. The 13F did its job the moment it put the name in front of you.
SIA tracks the portfolios of 15 elite investors — including Buffett, Seth Klarman and Bill Ackman — with every holding, its weighting, and the full quarter-by-quarter history of what they bought and sold, so the patterns are visible without reading raw filings.
Common questions
How often are 13F filings published?
Four times a year, within 45 days of each calendar quarter end. In practice that means filings appear in mid-February, mid-May, mid-August and mid-November.
Can I just copy Buffett's portfolio?
You can see the holdings, but you would be buying at unknown prices, without the reasoning, potentially months after the fact, and with no way of knowing when the position changes. Berkshire also holds assets no 13F captures. Copying a list is not the same as sharing a strategy.
Why is the data allowed to be so late?
The delay is deliberate. Immediate disclosure would let others trade against a manager still building or unwinding a position, which would make large positions more expensive to establish. The 45-day window is a compromise between public transparency and workable markets.
Are 13F filings reliable?
They are accurate about what they cover, since they are regulatory filings with legal consequences for errors. The risk is not inaccuracy but incompleteness — reading them as a full picture of what a manager owns.
The short version
A 13F shows the US-listed shares a large manager held at the end of a quarter, filed up to 45 days later. It excludes shorts, bonds, cash, foreign holdings and anything traded within the quarter, and it never explains a single decision. Read as a starting point for research it is one of the most valuable free datasets in public markets. Read as a shopping list it is one of the most misleading.
This article is educational and is not investment advice, and nothing in it is a recommendation to buy or sell any security. Avia Artis is not authorised or regulated by Finanstilsynet and is not registered with the SEC as an investment adviser or broker-dealer.
