A 13F filing is the quarterly report a large institutional investment manager files with the SEC disclosing the U.S. exchange-traded equity positions over which it exercises investment discretion. It is the public window into what hedge funds, mutual fund complexes, banks, pensions, and other large managers held at the close of a quarter. The obligation comes from Section 13(f) of the Securities Exchange Act and is implemented by Rule 13f-1.

The rule sets a bright-line threshold and a filing schedule.

"Every institutional investment manager which exercises investment discretion with respect to accounts holding section 13(f) securities, as defined in paragraph (c) of this section, having an aggregate fair market value on the last trading day of any month of any calendar year of at least $100,000,000 shall file a report on Form 13F with the Commission within 45 days after the last day of such calendar year and within 45 days after the last day of each of the first three calendar quarters of the subsequent calendar year."— SEC Rule 13f-1 (17 CFR 240.13f-1), source

Three boundaries define what a 13F does and does not show. First, the $100 million trigger is measured against the manager's aggregate holdings of “section 13(f) securities” — principally exchange-traded U.S. equities and certain options and convertible securities that appear on the SEC's quarterly Official List of Section 13(f) Securities. Holdings outside that list, including most short positions, cash, foreign-listed shares, and many derivatives, are not reported. A 13F is therefore a long-only snapshot of a specific universe, not a full balance sheet of the manager's book. Second, it is a quarter-end photograph filed up to 45 days later, so by the time it is public the positions may have changed. Third, the form reports positions, not intent; it does not say why a manager bought or sold.

What the information table contains

The substance of a 13F is its information table, which lists each reported security by issuer name and class, the CUSIP, the fair market value of the holding, the number of shares or principal amount, and the type of position, along with the investment discretion and any voting authority. Managers file the report as Form 13F-HR (holdings report) each quarter; a Form 13F-NT (notice) is used when another manager reports the holdings. Because every row carries a CUSIP and a dollar value, the filings aggregate cleanly across managers, which is what lets data users build quarter-over-quarter views of institutional ownership in a given stock.

The 13F regime has a defined history that shapes how the data is used. Congress added Section 13(f) to the Exchange Act in 1975, directing the SEC to collect and disseminate information about the securities holdings of large institutional managers so that the public and regulators could see the footprint of institutional money in the equity markets. The Commission set the reporting threshold at $100 million in covered securities and has kept it there, which means the population of filers has grown over time as asset values rose. The aggregate of all 13F filings is effectively a quarterly census of institutional long positions in covered U.S. equities — incomplete by design, but consistent and comparable across managers and quarters.

The covered-securities universe is the part of the 13F regime most often misread, so it is worth stating precisely what counts. Section 13(f) securities are equity securities of a class described in Section 13(d)(1) that are admitted to trading on a national securities exchange, together with certain equity options, warrants, and convertible debt that the SEC includes on its Official List of Section 13(f) Securities, which the Commission publishes quarterly. If a holding is not on that list, it is not reported on Form 13F. That single rule is why a manager's 13F can look nothing like its actual exposure: short positions, cash, most derivatives used to hedge, foreign-listed equities, and private holdings all fall outside the list and never appear.

The discretion test is the other boundary. The obligation attaches to accounts over which the manager exercises investment discretion, a term Rule 13f-1 ties to Section 3(a)(35) of the Act, and it extends to accounts over which any person the manager controls exercises discretion. A manager that merely advises without discretion, or that holds securities for which another manager reports, files differently — which is the role of the Form 13F-NT notice as opposed to the 13F-HR holdings report. The reporting is also additive across a complex: an asset manager with multiple advisory subsidiaries aggregates the discretionary accounts it controls to test the $100 million threshold and to build the information table.

Timing and confidentiality round out what a reader can and cannot infer. Because the report is due up to 45 days after quarter-end, a 13F describes a position as of a date already weeks in the past; a manager may have exited entirely before the filing is public. The SEC's rules permit a manager to request confidential treatment for certain holdings in limited circumstances, which can delay the appearance of specific positions. None of these features makes the 13F unreliable — it is an accurate record of the covered long positions a manager held on the stated date — but they bound the inference: a 13F is a lagged, long-only, covered-universe snapshot, and reading it as a real-time portfolio overstates what the filing claims.

The SEC amended the confidential-treatment and reporting mechanics over time, but the core design has held since Section 13(f) was added in 1975: give the public and the Commission a consistent, comparable view of large-manager equity holdings. For a reader, the practical use of a 13F is bounded by what the rule covers. It is authoritative for the long U.S.-equity positions a manager held at quarter-end and silent on almost everything else. Each report is retrievable on EDGAR by the manager's name or CIK, and the holdings table is the primary document behind any claim about what an institution owned.