The 45-day lag is the real story
Form 13F is filed within 45 days of quarter-end by every institutional money manager with at least $100M in U.S. equities. By the time you see the filing, the data is somewhere between 45 and 135 days old. A fund that "loaded up on NVDA" in their Q1 13F might have sold it all in February.
This is the single biggest mistake retail readers make: treating a 13F like a real-time portfolio.
What 13F includes — and what it doesn't
Included:
- Long U.S. equity positions (common stock, ADRs).
- Long calls and long puts (treated as equity equivalents).
- Convertible bonds.
Excluded:
- Short positions.
- Cash, futures, swaps, FX.
- Non-U.S. listed equities.
- Anything held in a separately managed account or external sub-advised mandate.
So when you see a hedge fund with a "long-only" 13F, that's not the fund — that's the subset of the fund that the SEC requires them to disclose. The actual book may be net short.
What to actually look for
When we surface a 13F change on OpenStocks, we focus on:
1. New positions — the manager has just initiated a stake, often after months of research. 2. Significant adds (>20% increase in shares) — high conviction signal, not just rebalancing drift. 3. Full exits — under-discussed but often the cleanest signal that thesis broke. 4. Concentration — when the top 5 holdings are >50% of the book, the manager is making a real bet.
What we avoid giving weight to:
- Small position trims (<10%) — usually mechanical.
- Index-tracking giants (BlackRock, Vanguard) — their 13F reflects passive flows, not opinion.
- Quarter-end window dressing — funds often clean up positions cosmetically before reporting.
The Berkshire exception
Warren Buffett's 13F is the most-followed filing on earth, and it has a unique property: Berkshire holds for years, often decades. The 45-day lag matters far less for him than for a quant fund. That's why "Buffett bought XYZ" still moves stocks even months later.
For most other funds, treat the 13F as a lagging sentiment indicator — useful for crowd dynamics, useless for trade timing.