What Is a 13F Filing?

• →Each position: issuer, share class, number of shares, market value at quarter end.
• →Call and put options on those securities.
• →It does not show short positions, bonds, foreign stocks, cash, or trades made after quarter end.

A position shown as of March 31 is reported by May 15. The manager may have sold it in April. This is why 13F data is best used for direction over time (a fund building or exiting a position across quarters) rather than as a same-day signal. It is most useful for managers who hold for years.

InsiderWatch diffs each new filing from a short list of notable managers against the prior quarter and alerts on material new positions, exits, and size changes, with the staleness stated in the alert.

• →Form 4: an insider's own trade, within two business days.
• →13D: a 5%+ stake with intent to influence, within five business days.
• →13F: a manager's whole US stock book, quarterly, 45 days late.

Filings are due 45 days after the end of each calendar quarter: mid-February for the December quarter, mid-May for March, mid-August for June, mid-November for September. Most large managers file on or near the deadline, so the last few days of each window are when the "what did Berkshire buy" stories appear. A manager can request confidential treatment for a position it is still building, and the SEC sometimes grants it; the position then appears in a later amendment, which is why an amended 13F (13F-HR/A) can be more interesting than the original.

Each row names the issuer, the class of security, a CUSIP identifier, the market value at quarter end, the number of shares or principal amount, whether the row is a share position or a put or call option, and how voting authority is split. The data has been filed in a structured format since 2013, which is what lets trackers diff one quarter against the next by CUSIP. There is no cost basis, no purchase date, and no indication of when within the quarter a position was bought or sold.

• →Short positions. A fund that is long a stock and short its competitor shows only the long.
• →Bonds, foreign-listed shares, currencies, commodities and most private holdings.
• →Cash, so a fund's equity book can look fully invested when half its assets are in Treasuries.
• →Anything bought after the quarter ended, or sold before the filing date.

The combination means a 13F is a partial snapshot of one side of a book, six to seven weeks old. It is excellent for seeing what long-term holders own and how their conviction changes over years. It is poor for guessing what a fast-trading fund is doing this week.

• →New positions and full exits matter more than size changes, because they are decisions rather than drift.
• →Measure size against the fund's own book, not in dollars. A $50 million position is a rounding error for a $100 billion manager and a top holding for a $1 billion one.
• →Watch for a position that grows across several quarters; that is a manager building with conviction, and the pattern survives the lag.
• →Check whether a value change came from buying or from the stock moving. The share count is the honest column.

InsiderWatch applies exactly this diff to a short list of notable managers and alerts on material new positions, exits and size changes, with the quarter-end date stated in the alert so the staleness is never hidden.