The Buffett Indicator

Total US stock market value as a percentage of GDP — one of the broadest single gauges of whether the market is expensive.

What is the Buffett Indicator?

The Buffett Indicator takes the total market value of a country's publicly traded stocks and divides it by that country's Gross Domestic Product (GDP). The result is a percentage: how big the stock market has grown relative to the real economy that ultimately supports it.

It is named after Warren Buffett, who wrote in a 2001 Fortune article (with Carol Loomis) that the ratio of total market value to GDP is "probably the best single measure of where valuations stand at any given moment." When the market's value races far ahead of economic output, future returns have historically been more muted; when it lags, they have tended to be stronger.

How to read it

There is no magic number that means "sell." The ratio has drifted upward over decades — markets have deepened, more companies are listed, interest rates fell for a generation, and US companies earn a growing share of their profits abroad (revenue GDP never captures). A reading that looked extreme in 1970 is closer to ordinary today.

That is why st-ox doesn't judge it against a fixed threshold. Instead it asks a simpler question — how far is today's reading from its own long-run average?

• Well below average — undervalued, historically cheap
• Around the average — fairly valued
• Clearly above average — overvalued
• Far above average, near historical extremes — significantly overvalued

The live gauge above places today's reading on exactly this scale. (For the statistically inclined: "how far" is measured in standard deviations from the average — but you don't need the maths to read the verdict.)

Why it matters for your portfolio

Valuation is one of the few things with a real track record of predicting long-run returns — not next week's price, but the average annual return over the following 5–10 years. A stretched Buffett Indicator doesn't tell you to sell; it tells you to temper your expectations, keep contributing steadily, and think about how much risk your plan actually needs. A cheap one is a tailwind for patient money.

That framing — expectations, not timing — is how st-ox presents it, alongside a price-vs-trend gauge and Tobin's Q on the Market Valuation page.

Limitations

• Flow vs. stock mismatch. Market cap is a snapshot of accumulated value; GDP is one year of output. The ratio compares two different kinds of number.
• Globalisation. US-listed multinationals earn much of their revenue overseas, which inflates market cap without lifting US GDP.
• Interest rates. Lower rates justify higher valuations, so the "fair" level shifts with the rate regime.
• US-only. This gauge is meaningful for the US market; other regions need their own history and context.

Frequently asked questions

For information and educational purposes only. Not investment advice, and not a recommendation to buy or sell any security. Data is sourced from FRED and may be delayed or revised.