13F Homework: how the quarterly 13F holdings changes are built
13F Homework reads every Form 13F holdings report in the SEC's bulk data sets and works out, stock by stock, which US investment managers opened, added, reduced or exited a position each quarter. Managers are sorted into style groups first, so an index fund's rebalance is not read like a concentrated manager's new position. It holds changes for seven quarter-ends, 2024-12-31 to 2026-06-30.
What you can do with it
- Rank stocks by most opened, most exited, net buyers, net sellers, change in holders or held value, and filter by sector.
- Click a stock to see which managers acted, who holds the most, and what its buyers also opened.
- Click a manager to see its top holdings and other moves.
- Compare the quarter's price range with the current price.
- Alerts: the most opened and exited stocks, stocks whose holder count doubled, and net buying by style.
Data sources
- SEC Form 13F Data Sets: one zip per quarter with the submission, cover page, information table and summary page of every 13F-HR, read according to the SEC readme.
- SEC EDGAR submissions for SIC industry, and SEC XBRL frames for shares outstanding.
- OpenFIGI for CUSIP to ticker; Yahoo Finance public chart data for prices; Sina Finance's US stock list for Chinese names.
Method
- Positions. Only common-stock long positions count; options feed only each manager's options share. Values are in US dollars, since the data starts in 2024Q3, after the SEC's 2023-01-03 switch from thousands.
- One filing per manager per quarter. Restatements replace the original and new-holdings amendments are added. Rows under other managers in the same CIK are merged by CUSIP.
- Change labels. Each position is new, add, trim, exit or hold against the previous quarter, with splits corrected by the median share ratio across holders. A CUSIP change is detected when at least 50 managers exit one CUSIP and at least 50 open another in the same quarter, with 60% or more overlap.
- Style groups. From each manager's number of holdings, top-ten concentration, turnover, options share, size tilt and similarity to the market-wide portfolio, rules assign one of nine groups, in this order: Index / passive, Options / derivatives, Concentrated, Event-driven / activist, Quant / systematic, Bank trust / wealth platform, Large-cap long-only, Small / mid-cap, Diversified active.
- Co-buying network. Among the 500 largest managers, two are linked when they opened or added the same stocks in a quarter (at least 0.2% of the portfolio, ETFs and funds excluded). Each shared stock is weighted by log(N ÷ managers buying it); a stock both opened counts 1.0, otherwise 0.5. A link needs at least 3 shared stocks, and each manager keeps its 8 strongest.
- Stock panel. A move is active when the stock's portfolio weight changed by 10% or more, otherwise in line. Percent of company is shares held ÷ shares outstanding.
Coverage and limits
- 13F has no shorts, bonds or non-US holdings, and filings arrive up to 45 days after quarter end.
- The quarter ending 2026-06-30 has 8,606 filers and 844 stocks in the stock list. Manager counts use all filers; named lists show the 500 largest.
- A manager with a new CIK after a reorganisation (Pershing Square Inc. is one case) shows every position as new. Exits of acquired companies count as real exits. Index trackers link strongly because index changes make them buy the same stocks.
- Nothing here is investment advice.
Update schedule
A script checks the SEC data set page every morning. When a new quarter appears it rebuilds everything and publishes; otherwise it refreshes current prices, last dated 2026-11-11. The SEC updates the data sets at the end of February, May, August and November.
FAQ
What is a 13F filing?
Form 13F is a quarterly report that investment managers with $100 million or more file with the SEC. It lists their US-listed long positions and options at quarter end, with shares and market value, but not short positions, bonds or non-US holdings.
How current is 13F data?
Managers can file up to 45 days after the quarter ends, and the SEC updates its bulk data sets at the end of February, May, August and November. Positions are quarter-end snapshots, so a manager may have traded since.
How do you tell an opened position from an added one?
Holdings are compared with the manager's previous quarter by CUSIP. A stock not held before is opened, more shares is added, fewer is reduced and none is exited. Splits and CUSIP changes are corrected first so they do not look like an exit plus a new position.
Which managers appear in the network?
The network and named lists show the 500 largest managers by reported value each quarter. Counts such as how many managers opened a stock include every filer, 8,606 in the quarter ending 2026-06-30.
Does a 13F show why a manager bought a stock?
No. A 13F shows what was held at quarter end, not the reason. The stock panel shows patterns instead, such as how much buying came from index or wealth-platform money and which buyers made it 3% or more of their portfolio, with links to the 10-K and news.