You don't have to be a millionaire to retire before 50, accountant says. Here's how she did it.

• Sonia Smith retired at 47 without millions, leveraging a side hustle and 401(k) savings.
• She worked for a multilevel-marketing cosmetics company to supplement her corporate income.
• Smith advises young people to invest early and seek financial advice for a smoother retirement.

Sonia Smith has extensive knowledge of how to make her dollars last a lifetime.

The 47-year-old retired from her 9-to-5 job as an accountant in June but didn't have $1.5 million in her bank account despite what some Gen Xers say they think is needed to retire before 50 .

In 2019, she began working for a multilevel-marketing cosmetics company to earn income outside her corporate job. Smith said she had two main financial goals that she aimed to achieve before retiring.

First, she wanted a reliable monthly income from her work with the makeup company, which she asked to remain unnamed for legal reasons.

"I wanted to achieve a financial status where I was bringing $10,000 into my home with my business that wasn't my 9-to-5," Smith told Business Insider.

While she's still working toward that goal, she eventually reached the point where she was earning as much from her side hustle as she was from her 9-to-5 after taxes.

Second, she planned for her 401(k) to reach at least half of five years' worth of her corporate salary. Smith said she started paying attention to her 401(k) "very early" in her career, and it paid off.

She's a married mother of three adult children. She and her husband live in San Antonio in a home they've owned since 2014.

"I wanted to make sure that I had the capability to pay my bill if something happened to the other people in my home," Smith said.

So she made her 401(k) a priority early by making sure she put money into it every week. It might sound simple enough, but one-third of US adults in a NerdWallet survey conducted in July said they planned to retire on Social Security alone , even though financial experts say it's a good idea to supplement the payments.

Smith isn't a millionaire and credits her experience working in finance and her side hustle with helping her leave the workforce early. She wasn't quite ready to retire when she did but decided to take a step back to look after her aging parents.

Investing is one area Smith said she wished she had explored sooner. She told BI that her 401(k) didn't reach the goal she'd set and that investing while she was still in her 20s might've made her retirement even smoother.

"My advice to anyone under the age of 30 who is wanting to retire before they're 60 is to get a financial advisor," Smith said.

The key, she added, is to "listen to what they say about how to invest your money because it's not just about a 401(k)." She advised young people to start looking into investment opportunities the minute they're hired somewhere.

Smith's retirement plan wasn't perfect, but it was effective when paired with the support system she has in her family.

Ultimately, she said, it's about doing the work to learn "how to make your money work for you."