Mutual funds remained the biggest holdings of self-directed 401(k) investors in the second quarter, according to Charles Schwab’s self-directed brokerage account indicators report, released Thursday.

SDBAs are brokerage accounts within retirement plans that participants can use to invest in securities that are not part of their retirement plan’s core investment offerings.

The report includes data collected from some 137,000 retirement plan participants who currently have balances between $5,000 and $10 million in their Schwab Personal Choice Retirement Account. Baby boomers made up approximately 42% of SDBA participants, Gen Xers 40% and millennials 11%.

Boomers allocated approximately 39% of their portfolios to mutual funds in the April-to-June period, followed by Gen X at 36% and millennials at 32%. Equities were the second-largest allocation for all portfolios, with Gen Xers allocating approximately 30%, boomers 29% and millennials 27%.

Millennials allocated a larger percentage of their portfolios to exchange-traded funds during the second quarter than did other generations: 23%, versus 19% for Gen Xers and 16% for boomers. Likewise with cash: 16%, versus 13% for both groups of older investors.

Boomers held about 3% of their portfolios in fixed income, while Gen Xers held 1% and millennials 0.5%.

Other Report Highlights

According to the report, the average SDBA balance for all participants in the second quarter was $265,902, up 1.5% from the first quarter and up 23% from the 2017 second quarter.

Boomers had the highest balances in their portfolios at an average of $365,561, followed by Gen Xers at $194,534 and millennials at $61,916.

Of participants who worked with an advisor to manage their PCRA, 46% were boomers, 42% Gen Xers and 8% millennials. PCRA users averaged 6.3 trades in the second quarter.

Mobile trades were equally popular among Gen Xers and millennials, with 19% of each generation using that method, compared with 14% of boomers.

Boomers on average held 11 positions in their SDBA, compared with nine positions for Gen Xers and seven for millennials.

U.S. broad funds were the most popular ETFs in the second quarter. All three generations held these three funds among their top five ETF holdings: Schwab U.S. Broad Market ETF, SPDR S&P 500 ETF and Vanguard Total Stock Fund.

As well, all generations continued to hold Schwab S&P 500 Index FD as their top mutual fund holding, followed by Schwab Total Stock Market Index.

Following are the top equity holdings as a percentage of assets held in equities across all generations:

Apple — Boomers: 8.7%; Gen X: 9.6%; Millennials: 5.7%

Amazon — Boomers: 5%; Gen X: 6.9%; Millennials: 7.6%

Facebook — Boomers: 2%; Gen X: 2.9%; Millennials: 3.2%

Berkshire Hathaway — Boomers: 2.6%; Gen X: 2.4%; Millennials: 1.8%

Microsoft — Boomers: 1.8%; Gen X: 1.3%; Millennials: 0%

Netflix — Boomers: 1.8%; Gen X: 2.5%; Millennials: 2.8%

Nvidia — Boomers: 1.4%; Gen X: 1.5%; Millennials: 1.5%

Alphabet — Boomers: 1.3%; Gen X: 0%; Millennials: 1.1% (each in Google A and C shares)

Alibaba Group Holding — Boomers: 1.2%; Gen X: 1.5%; Millennials: 1.5%

Bank of America — Boomers: 1.2%; Gen X: 1.6%; Millennials: 0%

Tesla — Boomers: 0%; Gen X: 1.4%; Millennials: 3%