S&P 500 Top-10 Concentration

## What this measures

The combined weight of SPY's ten largest holdings, as a percent of the fund. SPY holds the S&P 500 at index weights, so this is the index's top-ten concentration. Share classes count separately (Alphabet A and C are two holdings).

## Why it matters

Concentration is fragility. Above ~35% the index is a bet on ten companies; every regime that ended badly printed a peak here first.

## How to read it

Quarter-end points are exact: they come straight from SPY's Form N-PORT filing with the SEC. Between filings each day is an estimate: every one of the quarter's top 40 holdings is moved by its own price return since the quarter end, and the fund by SPY's. That is how index weights drift between rebalances, and it reset to the filed figure when the next filing lands (about 60 days after each quarter end). A rise means the index leans harder on a handful of names.

## What it does not say

It measures weight, not performance or valuation, and says nothing about when concentration reverses. Estimated days miss share-count changes, index additions and deletions, and quarterly rebalancing until the next filing.

## Source

SPDR S&P 500 ETF Trust (CIK 884394), Form N-PORT-P holdings filed with the SEC (sec.gov/cgi-bin/browse-edgar?action=getcompany&CIK=0000884394&type=NPORT-P). The SEC: "Information presented on sec.gov is considered public information and may be copied or further distributed by users of the web site without the SEC's permission." Daily estimates are Palanor's computation using licensed closing prices. Quarter-end values back to 2019; daily values from 2021.