Learn · Last updated September 8, 2026
How to Read a 13F Filing, Step by Step (Berkshire Hathaway Example)
Reading a 13F takes about ten minutes once you know where to look, and most of the value sits in a comparison the filing itself doesn't show you. Here is the process end to end, using Berkshire Hathaway as the example, plus the misreadings that trip up even experienced investors.
New to 13Fs? Start with the plain-English explainer: What is a 13F filing?
Step 1: Find the filing on EDGAR
Search the manager's name (or CIK, Berkshire's is 0001067983) on SEC EDGAR and filter by form type "13F". You'll see three kinds of entries:
- 13F-HR: the holdings report. This is the one you want.
- 13F-HR/A: an amendment. The cover page says whether it restates the whole report or adds to it. Getting this wrong double-counts positions.
- 13F-NT: a notice that another entity reports the holdings. The document itself is intentionally empty.
One trap here: large firms often file under multiple entities, sometimes 20 or more CIKs. If a famous firm's numbers look too small, you may be looking at one entity of several.
Step 2: Open the information table, not the cover page
Each filing bundles several documents. Skip the cover page and open the information table (the "Information Table" link on EDGAR's filing page renders it as HTML). One row per position: issuer, share class, CUSIP, market value, share count, put/call flag, discretion, voting authority.
Two unit traps:
- Values. Reported in thousands of dollars before a 2023 SEC change, in whole dollars after it. Some filers still get the convention wrong, which is why raw aggregators sometimes show funds with impossibly huge totals.
- Puts and calls. An options row reports the value of the underlying shares, not the premium. A put position is a bearish bet that looks like a holding if you skim.
Step 3: Read the shape of the portfolio
Sort by value, then look at the shape before any single name:
- Position count. Berkshire lists a few dozen positions. Bridgewater lists around a thousand. Same form, utterly different animals: one is a conviction portfolio, the other a diversified machine where no single line means much.
- Concentration. Berkshire's top 10 are roughly 90% of the reported portfolio. The more concentrated the book, the more each position tells you.
- What's missing. Cash, shorts, foreign listings, bonds. A 13F is the long U.S.-equity slice only. Berkshire's famous cash pile is invisible here.
Step 4: Diff against the previous quarter
This is the actual signal. A single 13F is a photo; the information is in the film. Pull the prior quarter and compare:
- New positions: names present now, absent last quarter. The headline event.
- Exits: the reverse, and often more informative than buys.
- Size changes: watch share counts, not values. Value moves with price even when the manager did nothing. A position whose value fell 10% while shares held steady wasn't sold, it just fell.
Doing this by hand means diffing two spreadsheets keyed on CUSIP. Tedious for a small filing, hopeless for a big one. This diff, including the share-vs-value distinction, is the core of what Whale's Nest automates.
Step 5: Apply the reality filters
- The 45-day lag. The snapshot is from quarter-end and can publish 45 days later. Positions may already be gone.
- Confidential treatment. The SEC can let managers delay disclosing positions they're still building; they surface in later amendments. If a famous filing looks oddly small, check for a subsequent /A.
- Turnover. Borrowing research ideas from a slow, concentrated value investor is defensible. Copying a high-turnover trader's quarter-old snapshot is noise.
- Options context. A big put against an index may hedge the long book you're looking at, not predict doom.
The classic misreadings
- Treating value drops as sales (check share counts).
- Reading a put position as a long.
- Missing sibling entities of the same manager.
- Double-counting amendment positions.
- Assuming the 13F is the whole portfolio.
- Treating a 45-day-old snapshot as current.
Structural claims here (form types, the units convention, confidential treatment, the 45-day window) come from the SEC's Form 13F FAQ and are verified against filings in our parsing pipeline. Nothing here is investment advice.
