Acorns, a eight-month old smartphone app built for exactly that purpose, said Wednesday that it had raised $23 million in additional funding.

Acorns’ app was designed to help people, especially first-time investors, get started in investing with small automated investments into a portfolio of exchange-traded funds, or ETFs, that the company selects and balances. Users link their bank accounts to the app, which then automatically rounds up the cost of all transactions to the nearest dollar, withdraws that spare change and invests it. For example, if you buy a coffee for $2.40, Acorns will take an extra 60 cents and invest it in an exchange-traded fund.

“We wanted to connect it to something you’re already doing, which is spending,” Acorns co-founder and CEO Jeff Cruttenden told Fortune. “What we see is that once people get started, they get in” – as in investing and using the app frequently.

Acorns’ two-pronged approach to making investing approachable by automating the process and incorporating a smartphone app is paying off with younger users. Of Acorns’ 650,000 registered customers, 75% are under the age of 35, Cruttenden said.

He added that of the $100 users invest monthly on average, $55 comes from through automated withdrawals using the formula involving the rounding up the value of transactions. It shows that people are drawn to this type of hands-off approach, he said. The rest of the money is from users making voluntary lump-sum investments.

“People are really understanding that technology can help them make better investing decisions,” Cruttenden said.

Acorns’ six portfolio options are designed with different risk levels, and are regularly and automatically balanced based on their performance. In recent years, other automated investment tools such as Wealthfront and Betterment have surfaced to offer investment management with little to no contact with human investment advisors. And an Acorns clone, Lawnmower, which invests in Bitcoin, the popular digital currency, launched last week.

Although Acorns is looking into offering tax-advantaged accounts and possibly more investing options eventually, it plans to stick to investing in ETFs for the time being. When asked what he thought about similar apps for investing like Robinhood, which lets people track and invest in public stocks from their smartphones and without paying fees, Cruttenden said he doesn’t see them as competition. Acorns’ automation is what’s appealing to users, he said. The alternative is traditional brokerage firms, which can be intimidating and have high fees and minimum investment amounts — Acorns’ minimum is $5.

Currently, Acorns charges a $1 monthly fee for accounts with a balance under $5,000, and 0.25% per year for accounts larger than that.

Father-and-son team Jeff and Walter Cruttenden, Acorns’ executive chairman, founded the Newport Beach, Calif.-based company in 2012. With the latest funding, the company has raised a total of $32 million. Greycroft Partners and e.Ventures led the recent round, with Sound Ventures, Garland Capital, and MATH Venture Partners also participating.

But despite the company’s growth and momentum, it could still face challenges when we inevitably hit a down market, said Mark Terbeek, a venture capitalist with Greycroft Partners who led the investment in Acorns. And despite the sign-ups for the service, less than half of those registered users end up funding their accounts.

“This us maybe the first time these individuals have ever had money invested,” he said. “There could be this reaction of ‘hey, this isn’t fun anymore.’”

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(Correction: An earlier version of this story, in one reference, misidentified an investor in Acorns. It is Greycroft Partners)