Institutional managers with over $100M in 13(f) securities file Form 13F-HR each quarter, within 45 days of quarter end, listing their US-listed long equity positions. The standard way to weight a position — used by Dataroma and most commentators — is:

weight = position value ÷ sum of the fund's 13F long book

It's simple and uses only the 13F itself. But a 13F is a long, US-listed equity disclosure only. It ignores cash, bonds, shorts, options, and foreign & private holdings. So whenever a manager's real book is larger than its 13F, this method overstates every weight: a fund that holds 40% cash looks fully invested, and its biggest equity stake looks like a far bigger bet than it is.

We weight each position against the manager's actual asset base, picking the best factual denominator available for that filer:

• Registered advisers — discretionary AUM. Form ADV Item 5F(2)(a): the assets the adviser manages with investment discretion, from the SEC's monthly adviser report. Labelled % of AUM.
• Insurance / holding companies — total investment portfolio. For Markel, the marketable equity & fixed-maturity securities plus cash & short-term investments reported in its XBRL filings, excluding operating-business assets. Labelled % of investments.
• Where that's the only reported base — shareholders' equity / partners' capital. For Berkshire Hathaway, whose ~$300B of short-term Treasury bills is not broken out as a queryable line in its XBRL data — so a clean total-investments figure can't be composed without guessing, and we won't. We use its reported shareholders' equity instead. Labelled % of equity.
• % of 13F only when no capital figure is disclosed at all — family offices, exempt or foreign advisers (Duquesne, Soros, TCI, the Gates Trust, Fairfax). These show no AUM column; the weight column simply reads % of 13F.

Why this is more directionally accurate: a 2% position means roughly the same thing across funds, and idle cash correctly shrinks the weights of a half-invested manager. Hover the ⓘ next to any AUM figure for its specific source.

• AUM is gross of leverage. Form ADV regulatory AUM counts longs, shorts, and borrowed capital, so a 2×-levered fund's weights look smaller than its true conviction. Net capital isn't publicly reported, so we don't estimate it.
• Form ADV updates roughly annually. RAUM changes only on annual ADV amendments, so within-year quarters reuse a stale denominator. On holding-history pages we match each quarter to the ADV snapshot reported on or before it, but the figure can still lag the real asset base by months.
• The base includes non-13F assets we can't fully see. AUM and investment portfolios contain bonds, cash, private and foreign holdings whose exact composition isn't disclosed — we know the total, not every line inside it.
• Corporate investment portfolios include insurance float. An insurer's securities book is funded partly by policyholder float, not shareholder capital, so % of investments answers “share of the portfolio” rather than “share of owners' money.”
• Some filers have no usable base at all. Foreign / IFRS filers (Fairfax) whose balance sheets aren't in SEC XBRL, and entities with no XBRL or no Form ADV, fall back to % of 13F.

% of 13F answers “what's big inside the disclosed equity book?” % of AUM / investments answers “how big is this bet relative to the whole operation?” Neither is wrong — they answer different questions. Both are available on every fund page via the weight toggle, and the source behind the denominator is always labelled.

Primary sources: SEC Form ADV (IAPD) and SEC EDGAR.

We parse each filing's information table directly from EDGAR (the latest amendment wins; confidential-treatment releases are merged in), aggregate duplicate CUSIPs, and exclude option positions. Values are reported in dollars since 2023, but some filers still use the old thousands convention — we detect this per filing via the implied price per share and normalize. Securities are identified by CUSIP and issuer name, not ticker; we resolve tickers via a curated CUSIP map and the SEC company directory. Quarter-over-quarter changes come from diffing consecutive filings, and history share counts are split-adjusted to today's basis where corporate-action data is available.

Company pages are served from stored read models, not live visitor-path SEC calls. When a SEC XBRL snapshot has been warmed, income statements, balance sheets, and cash flow statements come from company facts — the structured data behind each company's 10-K and 10-Q filings. When the licensed Intrinio read model is synced, Rockwood overlays its standardized and as-reported financials plus split-adjusted prices with attribution. Line items a company never reports are omitted rather than estimated.

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Nothing on this site is investment advice. Rockwood Research was built with AI from one person's direction — the code that fetches and parses SEC filings (13F-HR, XBRL company facts, Form ADV) is automated and AI-written, and is not reviewed figure-by-figure by an analyst. Errors can come from the filings, from that code, or both. Every figure links to its primary source on EDGAR; verify there before acting on anything.