One of the favorite ways of investing for millennials is growing up.

Wealthfront, one of the leading “robo-adviser” investment companies, doubled-down on its all-digital strategy on Thursday, even as its main rival went down a different path.

Wealthfront, which has about $4.65 billion in assets, overhauled its interface to bring in all kinds of customers’ assets, including the value of their homes, in what is the first major change since Chief Executive Andy Rachleff returned to lead the company in October.

The new system, called Path, was designed to show what people will need to save to retire, and how far away they are at their current pace, Dan Carroll, a co-founder and chief strategy officer, wrote in a blog post.

“Life comes at you fast when you hit your thirties,” he wrote.

Its rival, Betterment, on Tuesday, announced that customers, for a fee up to 0.5 percent a year, could get access to a real-life human adviser if they have more than $250,000 invested with the company.

For those who don’t want such a personal touch, a flat fee of 0.25 percent was introduced — which raised costs for about 20,000 users, Joe Ziemer, Betterment spokesman, told The Post.

That change upset some of their users.

“Hey @Betterment why increase fees 67% w/ ZERO added value at that level?” Twitter user Bryan Tilton wrote to the company. “Convince me to invest more, NOT betray your faithful with $$ grab.”

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