COUNTERPOINT · 1950—NOW — Top 10 Market Capitalization Share of Total U.S. Equity (1950–Present)
S&P 500 top-10 weight: 40.3% as of 2026-10-03.
Top 10 Portfolio Decay — Structural underperformance and decay exhibited by static buy-and-hold portfolios of decade-leading titans versus broad indexes.
The plate
Historical share of total market value held by the ten largest firms: 30% in 1963, 12% in 1993, 27% in 2023, and surpassing 33% in 2026, eclipsing the prior 1963 peak.
What this page answers
This static page is built to answer searches for COUNTERPOINT · 1950—NOW. It summarizes the live dataset behind the Top 10 Market Capitalization Share of Total U.S. Equity (1950–Present) panel and links to the full interactive chart.
Historical share of total market value held by the ten largest firms: 30% in 1963, 12% in 1993, 27% in 2023, and surpassing 33% in 2026, eclipsing the prior 1963 peak. The data is refreshed by the History of Market pipeline and published as a stable JSON endpoint for research, citation, and AI-agent use.
Data & Source
GET /api/latest/concentration.json — Canonical dataset endpoint.
Exchange closing prices · Company filings · Robert Shiller · FRED · NBER.
FAQ
Where does this data come from?
History of Market combines public market and macro datasets — exchange closing prices, company filings, Robert Shiller, FRED, NBER, and the UBS Global Investment Returns Yearbook (Dimson–Marsh–Staunton). The exact endpoint for this panel is linked below.
How often is it updated?
Daily-tier datasets refresh after the U.S. market close, with a broader weekly refresh on Sunday. The timestamp shown on this page comes from the JSON payload.
Can I use the data?
Yes, for research and education with attribution to History of Market. Upstream data sources retain their own terms.