Grizzly Bulls
← Grizzly Bulls Research

S&P 500 Concentration Lab

Explore S&P 500 concentration across history, market weight, earnings, valuation, operating fundamentals, AI-linked exposure, and forward-return sensitivity without flattening unlike measurements.
7 research views7 published source studies1965 to 2026 observation contextNo composite concentration score
S&P 500 concentration

Today's concentration is easier to interpret when market weight, fundamentals, valuation, and history stay in their own measurement lanes.

The reconstructed top-10 index weight was 38.24% in June 1965 and 38.15% in June 2025. In the newer issuer-weight snapshot, the ten largest issuers carry 40.45%. The ten largest covered revenue contributors generate 26.32% of the covered positive revenue pool and carry 24.97% of market weight, while capital spending's top-10 same-cohort gap is -30.79 pp.

38.15%June 2025 reconstructed top-10 index weight
38.24% at the June 1965 endpoint under the published historical reconstruction.
-30.79 pptop-10 capex same-cohort gap
Market weight minus covered positive capex share in the September 2026 study.
-0.72six-observation forward-return correlation
Falls to -0.04 when the 1965 observation is excluded.
The Lab coordinates published studies, but it does not synchronize their source dates, interpolate missing history, or combine unlike measurements into one score.

Explore current and historical concentration views

Use the view selector to move from historical top-10 concentration to current AI-linked exposure, earnings, valuation, fundamentals, same-cohort market comparisons, or the sparse forward-return study. Fundamental views also support metric and top-10/top-20 selection.

Selected view

Fundamentals vs. same-cohort market weight

Fundamental shares and market weights for the exact same top-10 or top-20 contributor cohorts.

Data through 2026-09-21Version 1.0
Revenue top-10 fundamental share26.32%
26.32
Cohort
Exact top 10 positive revenue contributors
Denominator
Covered positive revenue pool
Coverage
468/500 issuers (93.6%)
Revenue top-10 same-cohort market weight24.97%
24.9667
Cohort
Exact top 10 positive revenue contributors
Denominator
Normalized S&P 500 issuer market weight
Coverage
468/500 issuers (93.6%)
Revenue top-10 market minus fundamental gap-1.35 pp
Cohort
Exact top 10 positive revenue contributors
Denominator
Same-cohort market weight minus covered positive-pool share
Coverage
468/500 issuers (93.6%)
Overall market context40.45%Ten largest issuers by normalized S&P 500 market weight
Want the underlying fundamental concentration without the market comparison?

Company detail

10 published contributors
  1. #1 AMZNAmazon · Consumer Discretionary
    4.21%3.79% market · -0.42 pp
  2. #2 WMTWalmart · Consumer Staples
    4.15%0.72% market · -3.43 pp
  3. #3 UNHUnitedHealth Group · Health Care
    2.63%0.51% market · -2.12 pp
  4. #4 AAPLApple Inc. · Information Technology
    2.44%7.39% market · +4.95 pp
  5. #5 MCKMcKesson Corporation · Health Care
    2.37%0.15% market · -2.22 pp
  6. #6 GOOG/GOOGLAlphabet Inc. · Communication Services
    2.37%5.61% market · +3.24 pp
  7. #7 CVSCVS Health · Health Care
    2.36%0.17% market · -2.19 pp
  8. #8 XOMExxonMobil · Energy
    1.95%0.97% market · -0.98 pp
  9. #9 MSFTMicrosoft · Information Technology
    1.95%5.57% market · +3.62 pp
  10. #10 CORCencora · Health Care
    1.89%0.09% market · -1.80 pp

Sector detail

Published leading sectors
  1. Information Technology13.59% fundamental
    39.04% market+25.45 pp
  2. Health Care21.40% fundamental
    9.16% market-12.24 pp
  3. Consumer Staples11.64% fundamental
    4.36% market-7.28 pp
  4. Consumer Discretionary12.34% fundamental
    8.77% market-3.57 pp
  5. Energy6.32% fundamental
    3.38% market-2.94 pp
  6. Industrials10.15% fundamental
    8.07% market-2.08 pp

The fundamental and market bars use the exact same contributor cohort. The overall market figure is context only and is not substituted for that same-cohort market weight.

Open this exact Lab viewDownload selected view JSONCommercial data licensing

The portable JSON contains only the values in this selected Lab view plus their source, date, cohort, denominator, unit, and coverage context. It does not include underlying third-party source records or private review fields.

History and outcomes are coordinated, not merged

Historical structure

The historical view contains seven exact reconstructed decade endpoints from June 1965 through June 2025. The Lab does not manufacture quarterly values between those observations.

Open the historical study →
Forward-return sensitivity

Six non-overlapping decade starts are paired with the following 10-year annualized S&P 500 price return. The -0.72 sample correlation falls to -0.04 when 1965 is removed, so the result remains sensitivity evidence rather than a timing rule.

Open the forward-return study →

Same unit does not mean same measurement

Direct comparisons stay within compatible groups

A top-10 trailing-earnings share can be compared with the matched top-10 market-cap share from the same earnings study. A same-cohort revenue share can be compared with the market weight carried by those exact revenue contributors.

Context stays separate when cohort semantics differ

The historical top ten, overall ten largest issuers, top ten security lines, an AI-linked cohort, and top ten capex contributors are different groups even when every result is expressed as a percentage.

Where each published study sits in time

The Lab deliberately preserves different observation dates. Historical and forward-return studies run through June 2025, earnings uses March 2026, valuation uses June 2026, and the newest fundamental and market-weight work uses September 2026.

StudyLab viewData throughVersionDownloads
S&P 500 Concentration History: How the Top 10 Changed From 1965 to 2025Historical market concentrationJune 30, 20251.0JSON · CSV
S&P 500 Concentration and Forward Returns: Does a Top-Heavy Market Predict the Next Decade?Forward-return sensitivityJune 30, 20251.0JSON · CSV
S&P 500 Earnings Concentration: Are the Top 10 Backed by Profits?Earnings supportMarch 31, 20261.0JSON · CSV
S&P 500 Valuation Concentration: What Does the Index Cost Without the Top 10?Valuation splitJune 30, 20261.0JSON · CSV
S&P 500 AI Concentration: How Much of the Index Is AI-Linked?Current AI-linked concentrationSeptember 9, 20261.0JSON · CSV
S&P 500 Fundamental Concentration Atlas: Revenue, Profits, Cash Flow, and Balance SheetsFundamental concentrationSeptember 21, 20261.0JSON · CSV
S&P 500 Fundamental vs. Market-Cap ConcentrationFundamentals vs. same-cohort market weightSeptember 21, 20261.0JSON · CSV