The 3 most common financial mistakes young people make, according NerdWallet's self-made millionaire founder

NerdWallet CEO Tim Chen

Nobody's perfect when it comes to making financial decisions. Even billionaires like Warren Buffett make investment mistakes, so it's understandable when young people get off on the wrong foot.

Tim Chen, co-founder and CEO of the personal finance website NerdWallet, tells CNBC Make It that there are a handful of common financial mistakes he sees young people make all of the time.

"There's a few that drive me nuts," Chen, 35, says of the three most typical mistakes, though he's quick to add that they are nothing to be ashamed of, especially if you're not a financial professional.

"The commonality is usually that a normal human being wouldn't even know to ask these questions or think about these things."

1. Forgetting to rollover your 401(k)

The first mistake Chen highlights certainly seems pretty common, as many people allow retirement funds from previous jobs to collect dust instead of rolling over the investment into a new plan. Chen notes that some financial institutions charge fees of more than 1 percent a year just for managing your 401(k) plan. Those fees can continue to add up even if you're no longer contributing to the plan.

"You're basically going to lose a percentage of your money," Chen says. "Think about how much that compounds to over time. What you should do is roll it over to, basically, a zero-cost IRA and save thousands and thousands of dollars over the course of your life by doing that."

Even Chen wasn't immune to this financial mistake despite the fact that he has an economics degree from Stanford and he spent several years working for Wall Street hedge funds before founding NerdWallet in 2009, a site that sees 10 million monthly visitors and has been valued at more than $500 million. Chen says he "had no idea" how common management fees for old 401(k) accounts were until years after he left the hedge fund business and checked his own statements.

"I went back and looked at the fees finally, and I was getting charged 2 percent a year just for leaving my money in my 401(k)," he says.

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2. Not refinancing loans

Another mistake Chen identifies is when people don't look to change the terms of a loan — from student loans to money borrowed to buy a car — once their financial situations change.

"A lot of people don't realize that you can refinance almost any loan under the sun," Chen says. "Whether you're talking about your credit loan, your student loan, your auto loan, if you've borrowed money, there's always a chance to go refinance it at a better interest rate as your credit improves, or just as interest rates change."

While Chen says the most common type of loan that he sees people fail to refinance is an auto loan (people "should really keep an eye on that regularly," he says), student loan debt is also a major issue for young people. CNBC reported on May 5 that outstanding student loan debt in the U.S. has tripled over the last decade, reaching nearly $1.5 trillion in total, which is more than both auto and credit card debt.

Student loan debt can easily balloon, making it harder to save for other big purchases (like a house), but borrowers do have the option of refinancing their loans as their salaries and credit scores improve over time.

3. Bad budgeting

The final mistake Chen warns against is extremely simple, but still very common. It's "just spending more than you make," he says. There are a lot of different ways to set and follow a budget, but the most important part is simply making sure you're spending responsibly to avoid racking up debt.

"I think there's rational reasons to do it — you're only young once," Chen says of overspending. "But, you have to be responsible."

Of course, even Chen himself isn't completely immune to the occasional unwise purchases. The NerdWallet CEO says his least healthy (in more ways than one) financial habit is an addiction that combines food delivery and the gig economy.

"I just have this terrible, terrible habit with Uber Eats," says Chen, who estimates that he averages at least one food order from Uber Eats per day, "if you're counting the weekends."

"If I were to just be more disciplined about cooking," he says, "I could probably save thousands of dollars a month and I'd be so much healthier."

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