31-year-old millionaire who saves 50% of his income shares his No. 1 money-saving tip

This millennial went from broke to millionaire within five years
This millennial went from broke to millionaire within five years

When Grant of Millennial Money looked at his bank balance after graduating from college, he knew he had to buckle down.

With $2.26 to his name, he moved back in with his parents, landed a digital marketing job and started building websites on the side to complement his $50,000 salary. Within a year, Grant was making more money from his side gig than his full-time job.

"I was hooked and turned my side hustle into a digital agency that I still run today," the now 31-year-old, who goes by his first name exclusively, tells CNBC. "I've generated millions and millions of dollars in revenue growth across my clients."

Five years after taking a screenshot of his $2.26 balance, Grant hit seven figures.

While much of his financial success is due to the fact that he focused on earning and developing multiple streams of income, a key step to building wealth is saving, Grant says.

During his five-year journey to millionaire status, Grant saved 50% of his income. He didn't just save a ton of money — he put it to work. After all, "in order to build wealth you need to be making as much money as possible on your money," Grant writes on his blog.

Today, despite his financial success, he still focuses on living simply and sets aside 40% to 50% of what he makes.

The key to saving half your income, Grant says, is to make things automatic: "Automation is essential. When I first started saving and investing, I was a little more old school — I was trying to invest as much as possible into the online savings accounts I had set up and it was a pretty manual process. Now, one of the biggest recommendations I make is to automate as much of your savings as possible."

Grant of Millennial Money
Courtesy of Millennial Money

Today, there are a handful of apps and tools "that make it so easy to save without even thinking about it," the self-made millionaire says. He recommends talking to your HR department and having a portion of your income automatically sent to a savings or investment account. This is in addition to contributing to your 401(k), Grant notes.

You can also look into micro-investing apps that invest your "spare change." Acorns, for example, will round up your purchases to the nearest dollar and automatically put any spare change to work.

Grant isn't the only one who advises putting your financial plan on auto-pilot. As self-made millionaire David Bach writes in "The Automatic Millionaire," automating your finances is "the one step that virtually guarantees that you won't fail financially. … You'll never be tempted to skimp on savings because you won't even see the money going directly from your paycheck to your savings accounts."

Read more about how to link all of your accounts and automate everything.

Why Jay Leno never touched his 'Tonight Show' money
Why Jay Leno never touched his 'Tonight Show' money