It's too soon to dub 2022 the year of the side hustle: Research shows more Americans are likely to start their own in 2023.

Two in five Americans created or maintained at least one additional source of income in 2022, according to a survey from The Harris Poll and workflow integration company Zapier. That's a 6% increase over December 2020, a charge led mostly by millennials and Gen Zers, the same survey added.

Those millennials and Gen Zers might need the cash. Nearly half of them "live paycheck to paycheck and worry that they won't be able to cover their expenses," a 2022 Deloitte survey noted.

Side hustles can sometimes be just as draining as a full-time job — but they don't have to be. Last year, CNBC Make It spoke with several individuals who brought in up to millions of dollars per year on the side. Eight of them worked less than 20 hours per week to do so.

In analyzing them, a few themes emerge. Here are four of the most lucrative and least time-consuming side hustles that gained steam last year:

Online education

You might have skills that other people want to learn. Social media has proven an efficient way to teach them, and earn cash while doing so.

In 2020, Kat Norton was living with her parents when she launched Miss Excel, a TikTok account aimed to teach followers spreadsheet tips and tricks. After a couple of weeks, she hit 100,000, then started selling more excel courses from her website.

She quit her job in January 2021 after she started earning more through her side hustle than in her full-time management consultant role. Now, Miss Excel earns about $2 million per year, and Norton only works four hours per day.

Graham Cochrane has a similar story: He lost his audio engineer job in 2009 at age 26. He and his wife relied on savings and food stamps while he tried to launch his own production company.

Later that year, he started a music blog called The Recording Revolution that taught followers the ins and outs of the music industry. He grew his reach with YouTube videos and online courses.

Those courses continue to be successful, but his second business, which "teaches people how to monetize their knowledge and passions like I did," is how he earns most of his income. He now earns $160,000 per month for five hours of work per week.

Real estate

Renting out real estate typically comes with a high upfront cost — buying and setting up property can be pricey — but it can offer a steady stream of income for only a handful of work hours every week.

Wedding photographers Adriana Krause and Stephan Alvin spent about $487,000 buying and renovating homes near both their families: Alvin's in California, and Krause's in Rio de Janeiro. Krause and Alvin, a married couple, spend about six months of the year in each home while renting out the other.

In just five weeks of listing their Oakhurst, California, cabin, they brought in $13,000. The couple now only spends about an hour per week managing bookings, they say.

Even small properties can be effective investments in the right locations: Hawaii native Kehau Hall spent $8,000 setting up an Airbnb tent near a local volcano that now earns her $28,000 per year, for example. She works 10-15 hours per week managing, cleaning and checking in on the bookings.

Vending machines

You might be surprised to learn how lucrative vending machines are for their owners. Some of those owners are, too.

Before Covid hit, Quinn Miller was making $240,000 per year working for ad-tech startup in California. Then his clients disappeared and he struggled to meet his sales quota. After reading on Twitter that office vending machines could provide passive income, he bought two of them for a total of $5,000.

It took months for him to make the business profitable. Now, he spends six hours per week managing 57 vending machines, which bring in an average of $30,000 per month, as his full-time job.

Marcus Gram has a similar story: He wanted to create passive income, and after his friend watched a woman take wads of cash out of a vending machine, he knew where to start.

In 2018, he moved from Rochester, New York, to Philadelphia and bought two vending machines. He only made $5,000 in his first year, but continued to invest in the business. Three years later, he quit his $17-per-hour managerial job, and his 21 vending machines now bring in more than $300,000 per year.

Designing jewelry, t-shirts and other forms of apparel

Your creativity itself can be lucrative, if you're able to attract the right audience.

In 2016, Nicole Tocci, who owns a tanning salon in Berkeley Heights, New Jersey, started removing buttons from Chanel clothing and turning them into necklaces. She launched a website for her side hustle in late 2020, and now makes up to $41,000 per month from it.

Tocci knew the necklaces would be a hit for people like her salon customers, who already gravitated toward designer clothing. It only takes her 15-20 hours per week to source, make and list the jewelry online, as of November 2022.

These types of side hustles don't have to feature fancy designer brands. In 2014, Ryan Hogue was making $85,000 per year as a full-time web developer when he started searching for a second source of income. He decided to design and sell print-on-demand t-shirts — a relatively low-effort gig, he figured, because third-party vendors would handle the printing, packaging and shipping.

He designed and sold t-shirts on sites like All Sunsets, Creative Fabrica and Vexels before moving to Amazon. Business took off after he learned to track trends on the platform, helping him design shirts that would sell quickly based on what was in demand.

By 2020, he was making enough to quit his full-time job. Now, he makes $14,600 per month by working just one hour per day.

"I want people to know that they don't need a degree in graphic design to succeed in the print-on-demand business," Hogue wrote for CNBC Make It in November. "They just need a little bit of creativity and a lot of drive."

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