Money

If you want to retire by 40, you’re probably already behind, says financial expert

With stories of people achieving financial independence in their 30s and 40s saturating the Internet, the prospect of early retirement can begin to seem like an achievable goal. And for many, it can be — but only if you prepare early.

If you start saving in your 20s with the goal of retiring by 40, you'll need to aim to save and invest at least 50 percent of each paycheck to reach your goal. You should also put at least part of any bonuses or stock options toward your growing retirement fund.

But even if you're a diligent saver, if you're starting the process after you've already established a life and a career, you're probably already a step behind, Kimmie Greene, money expert at Intuit and spokeswoman for Mint.com, tells CNBC Make It.

Greene recommends making early retirement your goal from the outset of your professional life and arranging everything else around it, including where you live and which industry you work in. That means starting to plan as early as in college, when you begin exploring your interests and career choices.

"It's hard to say, 'Yeah I wanna do this by age 40!' because it's going to take a job that has a salary that not only covers your expenses but leaves extra for savings," Greene says.

While there are always exceptions to the rule, to take on such an aggressive goal means filtering every other decision through that goal. Do you want to live in an expensive city like San Francisco or a more affordable one like St. Louis? Do you plan to work in a lucrative industry such as tech or finance or do you have your heart set on social work?

If you have kids, do you live near family members who can help out with childcare or will you pay for everything out of pocket?

Early retirement requires sacrifices, whether it's living in a less flashy but more affordable city, dedicating your free time to a side hustle or waiting a few years to have kids so you can maximize your savings. It comes down to a simple principle: You can afford some things but not everything.

"You're probably not going to be able to be a journalist in Manhattan with two kids and retire by 40," Greene says.

While a getting a head start with retirement planning helps if you want to settle down early, it doesn't mean you're doomed if it wasn't your focus at 18. Greene emphasizes that whenever you decide to aim to retire in your 40s, you should take a deep look into your current situation and create a plan.

"Whether you're making $55,000 or $200,000, you say, 'Okay this is what it looks like and how do I want to live today to make sure that I'm putting that money away?'" she says.

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