A software engineer invested his way to retirement at 30 in nine years, then wrote about the math

Mr. Money Mustache tracked his and his wife's net worth ("the Stash") from a starting salary of $41,000 and zero net worth at age 22 in 1997 through retirement nine years later. By year one his salary had risen to $57,600 and the Stash stood at $5,000; by year two it was $23,000 ($13k in cash/shares, $10k in retirement accounts).

In year three, after a job change pushed his income to $77,000, the couple bought a $235,000 house in Boulder, Colorado, with a $47,000 down payment, bringing the Stash to $67,000 ($47k home equity, $10k retirement, $10k cash). Combined household income climbed to $83,000 (him) plus $44,000 (his wife) by year four, with the Stash at $150,000; by year five, combined income hit roughly $160,000 and the Stash reached $250,000. It continued to $365,000 in year six and $490,000 in year seven.

By year eight, with his income at $125,000 and his wife's at $70,000, the Stash hit $600,000. In year nine he quit his job to start a house-building company earning about $50,000 in its first year, while his wife earned $60,000; the Stash reached $720,000. Throughout, the couple lived on a shared $30,000-40,000 a year including housing -- a figure he attributes largely to living close to work -- later narrowing to about $22,000-24,000 once their house was paid off. They maxed pre-tax retirement contributions of $16,500+ annually, captured employer matching, dollar-cost-averaged into the S&P 500 in taxable Vanguard accounts, and bought a second, cheaper house in year nine while renting out the first for positive cash flow, which generated about $2,400 a month in passive income -- more than their living expenses.