Global Equity ETFs: When the US Weight Outruns the US Economy

A global equity ETF weighted by market capitalization mirrors the hierarchy of stock markets, not the size of economies. That hierarchy now gives the United States a weight more than twice its share of world output.

Three measures put a number on the gap: the US weight in the main global index, the US share of all listed companies worldwide, and the US share of world GDP. They do not say the same thing.

Three weights for one country

The MSCI ACWI is the benchmark of most global equity ETFs. In the latest N-PORT filing of a fund that tracks it (SEC EDGAR, holdings at July 31, 2026), US issuers made up 61.4% of net assets, Japanese issuers 5.0% and British issuers 3.2%.

A broader measure gives a lower figure. In 2025, US listed domestic companies were worth $68.9 trillion out of $141.3 trillion worldwide. That is 48.8%, according to World Bank data compiled from the World Federation of Exchanges (market capitalization of listed domestic companies). The same year, the United States produced $30.8 trillion of a world GDP of $118.4 trillion: 26.0%.

The ETF weight exceeds the GDP weight by 37.6 points. Two layers explain it. Markets first: US companies are worth far more relative to output than companies elsewhere, which accounts for the 22.8-point gap between market share and GDP share. Then the index: the ACWI keeps only large and mid caps across 47 markets and covers about 85% of the global investable universe, which lifts the US weight by another 15 points over the exchange-wide measure.

The second layer is the one investors see least. It owes nothing to prices: it comes from what the index chooses to include, and it changes only when the rules or the eligible universe change.

How the gap built up

The current imbalance is not permanent history. In 1988 and 1989, at the height of the Japanese bubble, US companies represented 29.4% and 29.3% of world market capitalization, barely above the US share of GDP (26.7% and 27.6%). The US share then climbed to 52.6% in 1998, fell to 31.8% in 2009 after the financial crisis, and rose for fifteen years to 54.0% in 2024.

That 2024 peak put the gap with the GDP share at 27.8 points, the widest since 1980 on World Bank data, whose early years cover fewer exchanges. In 2025 the US share eased to 48.8%: the value of US listed companies rose 11% in dollar terms, while the rest of the world gained 37%. A cap-weighted global ETF adjusts automatically, because its weights follow prices.

The weights follow prices, by design.

That mechanism cuts both ways. When US stocks outperform, their weight rises and new money entering a global fund goes increasingly to them, a pattern traced in the analysis of equity ETF flows. When they lag, as in 2025, the same rule reduces exposure without any decision by the holder.

What sits inside the US weight

The US slice is itself concentrated. On August 31, 2026, the ten largest constituents of the S&P 500 made up 37.84% of the index, according to S&P Dow Jones Indices. In a global ETF, those ten companies therefore weigh close to a quarter of the whole portfolio (63.6% times 37.8%). This is an approximation, since the ACWI’s US segment and the S&P 500 do not hold exactly the same stocks.

Earnings back part of that weight. The net profit margin of the S&P 500 reached 17.0% in the second quarter of 2026, well above its five-year average. That is a record since FactSet began tracking it in 2009, according to its Earnings Insight of October 2, 2026. The forward price-to-earnings ratio stood slightly below its five-year average. On that measure, the premium rests more on profits than on multiples.

The rate backdrop has shifted under it. The Federal Reserve raised its target range to 3.75%-4.00% on September 17, 2026. The European Central Bank lifted its deposit rate from 2.00% to 2.50% in two steps, on June 17 and September 16, 2026, according to the ECB deposit facility rate. The 2010-2024 run of US outperformance had unfolded mostly with policy rates near zero.

Reading the gap without forecasting it

A wide gap between market weight and economic weight does not date a reversal. US corporations earn part of their profits abroad, 26.4% in 2025 against 35.8% in 2019 according to the BEA, so GDP understates their economic base. The depth and openness of US markets justify part of the index premium. The gap stayed above 15 points from 2013 to 2025 on World Bank data without closing.

Two series are enough to follow it. The first is the pair of World Bank shares, US market capitalization and US GDP as a share of the world, published annually. The distance between them measures how far valuations have pulled away from output. The second is the US weight in the ACWI factsheet, published monthly; its gap with the exchange-wide share measures what index construction adds. A narrowing first gap describes markets converging; a stable second gap describes index rules unchanged.

The choice of vehicle comes down to index construction, set out in the framework for reading an ETF, and to the liquidity of what the fund holds, discussed in the gap between ETF liquidity and underlying markets. In 2025 the world’s listed companies gave the United States less than half their value, and its main global index still gave it close to two thirds.

Last updated — 8 October 2026