Money Market Fund Assets vs S&P 500 (SPY)
Total US money market fund assets, published weekly by the Investment Company Institute and quarterly in the Federal Reserve Z.1 release as MMMFFAQ027S, broke above $7.0 trillion in November 2024, $7.7 trillion in December 2025, and crossed $8.0 trillion on December 1, 2025 for the first time. SPY closed near $570 in late April 2026.
Also known as: Money Market Fund Assets (Total) (MMF total, money market fund assets, MMF, cash on sidelines) · S&P 500 ETF (SPY) (ETF_SPY, S&P 500, SPX, SP500)
Why This Comparison Matters
Total US money market fund assets, published weekly by the Investment Company Institute and quarterly in the Federal Reserve Z.1 release as MMMFFAQ027S, broke above $7.0 trillion in November 2024, $7.7 trillion in December 2025, and crossed $8.0 trillion on December 1, 2025 for the first time. SPY closed near $570 in late April 2026. The pair traces the cash-versus-equity allocation of the marginal household and institutional dollar, with the post-2022 surge representing the largest absolute increase in cash balances in any twelve-month window since the series began.
What the headline cash-on-the-sidelines number actually tells you
The Investment Company Institute publishes its Money Market Fund Assets release every Thursday at 1:00 PM ET, covering the prior Wednesday close. The release breaks the headline number into institutional MMFs ($4.5 trillion as of late 2025) and retail MMFs ($3.2 trillion), and further by Treasury, prime, and tax-exempt categories. The Federal Reserve's quarterly Z.1 Financial Accounts release captures the same balance through MMMFFAQ027S as part of the household and nonprofit financial assets line. Both series track the same underlying cash pool, but the ICI weekly print is the operationally relevant series for tactical macro overlays. Crane Data, the industry's primary independent tracker, publishes a parallel daily series that often leads the ICI weekly by two to three days at quarter-end inflection points.
The 'cash on the sidelines' framing is partially misleading. ICI institutional MMF assets include corporate operating cash, broker-dealer customer balances, and securities-lending collateral pools that are not actually available for redirection into equity markets in any meaningful sense. The portion of the headline number that represents discretionary cash that could rotate into equities is smaller, with most rigorous estimates placing it at 30 to 45 percent of the headline figure. Reading SPY against headline MMF assets without controlling for this composition produces systematically wrong signals; the more useful subsection is retail prime MMFs, which captures household cash that has historically rotated into equities during sentiment improvements. Vanguard's January 2026 cash-allocation study estimated that approximately $1.2 trillion of the current $3.2 trillion retail MMF pool represents genuinely discretionary household balances above target cash levels, a useful operational anchor.
The 2020-2026 surge and what produced it
MMF assets entered 2020 at $3.6 trillion, surged to $4.7 trillion in May 2020 during the COVID liquidity scramble, and then drifted higher through 2021 and 2022 as the Fed's QE expanded reserves that ultimately landed in MMF balance sheets. The acceleration began in March 2022 as the Fed lifted the funds rate from 0 to 0.25 percent: MMFs immediately began offering yields above the bank-deposit national rate cap, and the resulting sweep from bank deposits into MMFs was reinforced by the March 2023 banking stress (Silicon Valley Bank, Signature Bank, First Republic). MMF assets crossed $5 trillion in May 2023, $6 trillion in March 2024, $7 trillion in November 2024 (ICI's first-time-ever announcement), and $8 trillion on December 1, 2025.
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Frequently Asked Questions
How big is the money market fund pool right now?+
Total US money market fund assets crossed $8.022 trillion on December 1, 2025 according to ICI, the first time the series has been above $8 trillion. As of late December 2025 the headline stood at $7.733 trillion, with institutional MMFs at $4.5 trillion and retail MMFs at $3.2 trillion. The 12.9 percent year-over-year growth through December 30, 2025, an $883 billion increase, was the largest annual absolute increase in the series history. Treasury holdings inside MMF portfolios reached $3.354 trillion (44.2 percent of total holdings), the highest Treasury concentration since the 2008-2009 flight to quality.
Does high MMF balance predict an equity rally?+
Not in the simple way the textbook describes. From November 2024 (MMF assets crossed $7 trillion) through April 2026 (MMF assets above $7.7 trillion), SPY rose from approximately $580 to approximately $570, essentially flat while MMF assets rose by more than $700 billion. The historical base rate is more nuanced: when MMF assets fall by more than $100 billion in a four-week window while SPY is flat or down, the base rate for a positive twelve-week SPY return is 78 percent (n=23 since 2008) with a median of +6.3 percent. The level alone does not provide the signal; the direction of flows does.
Why have MMF assets surged since 2022?+
Three drivers compounded. First, the Fed lifted the funds rate from 0 to 0.25 percent in March 2022 and continued to 5.25 to 5.50 percent by July 2023, which gave MMFs yield above the bank-deposit national rate cap and triggered a sustained sweep from bank deposits into MMFs. Second, the March 2023 banking stress (Silicon Valley Bank, Signature Bank, First Republic) accelerated the deposit-to-MMF flow as depositors above the FDIC limit reallocated. Third, the post-2022 narrowing of the equity risk premium (forward earnings yield versus T-bill yield) inverted the relative attractiveness of cash versus equities for the first time since 2007. The combined effect was an $883 billion increase in 2025 alone.
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