[!todo] Seed note. A starting point, not a finished note yet.
Float-adjusted market cap multiplies a company’s share price by only the shares available to the public, excluding blocks held by insiders, governments, and strategic corporate owners. S&P captures this with the Investable Weight Factor (IWF), the public fraction of shares. The point is that an index should weight a stock by how much of it investors can actually buy: if 60% of a company is closely held, weighting by total shares would force funds to chase a tiny tradable float and distort prices. The S&P 500 switched from total-cap to float-adjusted weighting in 2005. Seeded from S&P 500.