Cody Berman achieved financial independence by following a simple rule: Keep your expenses below your income and invest the difference.

Between various side hustles and entrepreneurial ventures, he widened the gap between what he earned and what he spent throughout his early 20s. By 2021, shortly before his 26th birthday, Berman said he had about $500,000 invested in the stock market, 13 rental units producing about $3,700 a month in cash flow, and a digital-products business earning more than $10,000 a month.

That was the point when he considered himself financially independent.

Business Insider reviewed screenshots of Berman’s Vanguard, Schwab, and Empower accounts showing that his net worth…