What it measures
The Bubble Memory is the average historical-percentile rank of three crowd-and-leverage indicators: NYSE/FINRA margin debt (dollar terms), S&P 500 dividend yield (inverted — low yield = high mania), and household equity ownership as percent of household financial assets. When all three sit near all-time highs, the index reads near 100. When they sit near long-run norms, near 50.
Why these three
Margin debt is the cleanest single read on whether the crowd is leveraged. Dividend yield (inverted) captures the implied participation premium — investors only accept low yields when they believe price appreciation will compensate. Household equity ownership share is the slow-moving bedrock — when over half of household financial assets sit in equities, the buying pool is structurally exhausted. Together they answer: who is already in, and how levered?
How to read it against Mania
The Bubble Memory is designed as the sister index to the Mania Index. Mania measures the multiple — price relative to earnings and economic substance. Bubble Memory measures participation — leverage and crowd composition. The 2000 dot-com peak read high on both. The 2007 GFC peak read moderately high on Mania but very high on Bubble Memory (margin debt and household equity ownership were extreme). The current reading: both running hot.
What it does not say
Participation can stay elevated for years. The 1990s ran with high household equity ownership for nearly a decade. This index, like Mania, tells you the conditions for a re-rating exist, not when. The discipline is to read it against Mania and against the Real Rate Index to triangulate where the cycle stands.
Revision — 25 September 2026
On 24 September the household equity share was rebuilt on the Federal Reserve's current Financial Accounts (Z.1) series, because FRED removed the series it had been built on. Margin debt was brought up to date in the same change. Every reading since June 2026 had been computed on the old, frozen inputs, so those readings were recomputed on the rebuilt data and the chart no longer jumps on 24 September. The historical reference readings before 2026 are unchanged. The index read 67 before this revision and 80 after.