As someone in my 30s, it’s tough to read tips for new grads without cringing. Too often, what now seems like obvious, common-sense advice is something that I blissfully ignored in my 20s.

Every once in a while, though, I get a little jolt when I realize that a younger version of me managed to do something right.

That’s how I felt when I read my colleague Cheyenne Devon's recent writeup from a chat with Ramit Sethi, a self-made millionaire and author of “I Will Teach You to Be Rich.” In it, he offers his No. 1 money tip for new grads.

“You’ve got to invest 10% of your salary every year,” Sethi says. “And at the end of the year, increase that by 1%. Do this for as long as you can and you will be a multimillionaire.”

Hey — I did that! Well, more or less. I didn’t exactly launch a career the second I graduated. I spent a few months making ends meet as a cater-waiter while crashing on friends’ couches. Even if I had money to spare, I wouldn’t have known how to invest it.

Luckily, I landed an internship at a financial magazine with a cubicle next to the editor who helped choose mutual funds for the company 401(k). Soon, 10% of my $12-an-hour salary went into the plan.

The key for new grads isn’t necessarily a particular percentage: It’s starting early and staying consistent. You’ll see a lot of quotes touting the “magic” of compounding interest or calling it the eighth wonder of the world. Really, it’s just math. 

You can use this calculator to see just how powerfully that math works in your favor if you start early.

Say you started contributing $300 a month to a workplace retirement account at age 22 and invested for the next 45 years. If your portfolio earned an annualized return of 7%, you’d end up with a balance north of $1.1 million. 

If you invested the same amount and earned the same return, but instead started at age 30, you’d end up with about $632,000. 

If you're graduating this spring, do yourself a favor and get started soon. Your future self will thank you.

CNBC