13F filings explained: how to read what hedge funds own

Every institutional manager over $100m must disclose their US equity holdings quarterly. Here's what a 13F contains, the four things it deliberately hides, and how to use it without being misled.

2026-08-05 · 12 min read · By Insider Option

Twice a decade, someone discovers that Warren Buffett's holdings are public information and concludes that beating the market is a solved problem. The filing they have found is Form 13F, and it is genuinely useful — but it is a photograph of a moving object, taken 45 days ago, with most of the frame cropped out.

This post covers what a 13F actually contains, the four categories of thing it structurally cannot show you, and how to extract signal from it anyway.

Who files, and when

Section 13(f) of the Securities Exchange Act requires any institutional investment manager exercising discretion over at least $100 million in "Section 13(f) securities" to report those holdings quarterly. That captures hedge funds, mutual fund complexes, pensions, endowments, insurers, family offices above the threshold, and bank trust departments.

The threshold has not moved since 1978, which is why the number of filers has grown enormously in real terms — $100m in 1978 is a far smaller fund than $100m today.

The deadline is 45 days after quarter end. So the 31 December holdings become public around 15 February. A position the fund opened on 2 October and still held on 31 December appears roughly four and a half months after it was established — and it may have been sold in January.

What is in the filing

A 13F has a cover page and an information table.

The cover page names the filer, the report period, and the filing type — 13F-HR (holdings report), 13F-HR/A (amendment), or 13F-NT (notice, meaning "another filer reports my holdings"). A 13F-NT with no corresponding holdings report is a dead end many screeners mishandle.

Each row of the information table gives:

• Name of issuer and title of class — e.g. "COM" for common stock, or "CALL"/"PUT" for options.
• CUSIP — the security identifier. This is what you join on; issuer names are inconsistent across filers.
• Value — market value at quarter end. Note that filings before 2023 reported this in thousands and newer ones in whole dollars, a transition that produced a great deal of nonsense in derived datasets.
• Shares or principal amount.
• Investment discretion — sole, shared-defined, or shared-other.
• Voting authority — sole, shared, or none, split into three columns.

Since 2023 the SEC requires 13Fs in structured XML, so the data is machine-readable without parsing tricks. Historical filings are messier.

The four things a 13F does not show you

This is the part that matters, and the part that most "follow the smart money" content omits.

1. Short positions

Not reported. At all. A fund showing a $500m long in an airline may be running a pairs trade against another airline, or hedging with index puts sized to make the position net flat. You are seeing one leg of a trade whose other legs are invisible.

2. Everything that is not a US-listed equity

No bonds, no cash, no commodities, no currencies, no foreign-listed shares, no private holdings. A macro fund whose actual thesis is expressed in rates and FX will file a 13F that looks like a small, random equity book — because the equity book is incidental to what they do.

3. Position size relative to the fund

You can compute a holding's share of the reported 13F portfolio, but not its share of the fund's total capital, because you do not know the denominator. "It's 8% of their 13F" is not "it's 8% of their book" unless the fund happens to be long-only US equity.

4. Anything that happened after quarter end

The report is a single-date snapshot. Intra-quarter round trips are invisible: a fund could have bought and fully exited a large position in November and the December 13F would show nothing. Conversely a position shown may already be gone.

There is also confidential treatment — a filer can ask the SEC to withhold a specific position temporarily, typically while accumulating. Granted requests surface later as amendments, which is why a fund's history can change retroactively.

How to actually use 13F data

Given all of the above, the useful applications are narrower than the marketing suggests — but they are real.

Concentration in a long-only manager

The limitations bite hardest for hedge funds. For a manager who is structurally long-only US equity — some value shops, many endowment-style portfolios, Berkshire's equity book — the 13F is most of the portfolio, and reading it is meaningful.

Change, not level

A holding's presence tells you little; a 60% increase in share count quarter-over-quarter tells you something. Compute deltas across consecutive filings and rank by conviction change rather than by dollar value. New positions and full exits are the highest-information rows.

Clustering across independent managers

One fund buying is idiosyncratic. Eleven unaffiliated managers with dissimilar strategies all initiating in the same quarter is a fact worth explaining. This is the same logic that makes cluster buying the strongest variant of insider Form 4 signals.

Ownership structure of a stock you already like

Inverting the question is often the best use. Rather than "what does this fund own", ask "who owns this stock, and are they patient capital or fast money". High turnover in the holder base is a different risk profile than a stable one, and it is visible in the aggregate 13F data.

13F vs the neighbouring filings

• Schedule 13D — crossing 5% ownership with intent to influence control. Due within five business days under the 2024 amendments (previously ten calendar days). Far more timely than a 13F and far more informative about intent.
• Schedule 13G — crossing 5% passively. Longer deadlines, less signal.
• Form 4 — corporate insiders, two business days, exact prices. See the Form 4 guide.
• N-PORT / N-CSR — registered funds report monthly and semi-annually with more complete coverage, including derivatives and shorts. For mutual funds and ETFs this is strictly better data than a 13F.

If timeliness is what you want, note the ordering: Form 4 at two business days, 13D at five, 13F at 45, and Congressional PTRs at 45 as well. The 13F is the least timely of the major ownership disclosures, despite getting the most attention.

Getting the data

All 13Fs are free on EDGAR. Filter a filer's EDGAR page by form type "13F-HR", or pull the quarterly full-index files if you want everything. Practical notes for anyone building on it:

• Join on CUSIP, never on issuer name.
• Handle the thousands-vs-dollars value convention change, or your historical series will be off by 1000×.
• Reconcile amendments — a 13F-HR/A may restate or merely add.
• Watch for 13F-NT filers and follow through to the reporting entity.
• Deduplicate affiliated filers; large complexes file under multiple CIKs and naive aggregation double-counts.

You can browse parsed institutional holdings on Insider Option's institutional page if you would rather not build the pipeline.

The one-sentence version

A 13F tells you what a manager's long US equity book looked like on one day at least 45 days ago, with no shorts, no hedges, and no denominator — which makes it excellent for generating research questions and poor for generating trades.

This post is for informational purposes only and is not investment advice. See our disclaimer.