Market strategists worry that the inflow of money could signal that the rally is getting old and finally dragging the last bears in off the sidelines, a classic capitulation sign.
"As the stock market continues to soar, it is attracting more money into stocks. That's what usually happens during meltups," Ed Yardeni, founder of Yardeni Research, said in a blog post Friday. "The flow-of-funds case for a meltup is mounting as more hot money pours into equity ETFs."
"Meltup" refers to a sudden influx of investor cash based on momentum or sentiment rather than fundamentals. Melt-ups often precede meltdowns.
BofAML's count shows that stock-focused funds — both ETFs and mutual funds — have pulled in a net $294.7 billion year to date. Excluding mutual funds, the inflows to their passive counterparts have totaled just more than $448 billion. The big shift to passive comes even though stock pickers have had a comparatively good year, with 49 percent of large-cap fund managers beating their benchmarks, according to Goldman Sachs.
The most recent surge in ETFs came from some of the $3.4 trillion industry's most popular names.
The SPDR S&P 500 Trust fund pulled in just shy of $10 billion over the past week, the iShares S&P 500 Value ETF gained $2.2 billion and the iShares Mid-Cap 400 Value ETF grabbed about $1.4 billion, according to FactSet. Year to date, the iShares Core S&P 500 has been the big winner, with $31.6 billion in inflows as the $142.9 billion fund has returned nearly 20 percent.
While pouring money into other areas, investors last week yanked $2.2 billion out of the iShares Russell 2000 ETF, which tracks the small-cap index.
Professional investors have provided much of the enthusiasm for the market. The Investors Intelligence survey, which gauges sentiment from investing newsletter authors, has found bulls outnumbering bears at around the same level as just before Black Monday in October 1987, when the Dow lost 22 percent in a single day.
In fact, investors continue to hedge their bets, with inflows to bond funds totaling $348.1 billion this year even as performance between stocks and fixed income is at its biggest disparity on record.
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