Kevin O'Leary, the Shark Tank investor, says the math of building wealth is not complicated. Save 15% of every dollar earned — paychecks, side hustles, even birthday money — and invest it in the market. Let compounding do the rest.
"If you make $68,000 a year, the average salary, and you do this your entire life, just 15% of your paycheck, you'll end up a millionaire at retirement at 65," O'Leary said in an Instagram video.
The numbers come first. At $68,000 a year, 15% works out to $10,200 annually, or $850 a month. Invested from age 25 to 65 at the S&P 500's historical average return of roughly 10%, that contribution grows to approximately $5.3 million by retirement, according to Fortune's calculations. Even a more conservative 7% return still delivers millionaire status, around $2.2 million.
The advice tracks with Warren Buffett's long-standing guidance. "Put 10% of the cash in short-term government bonds and 90% in a very low-cost S&P 500 index fund," Buffett wrote in a 2013 shareholder letter, arguing that approach beats most high-fee managers over time. Suze Orman has likewise urged Americans to save or invest at least 10% of earnings annually.
But the gap between the rule and the household budget is real. For a $68,000 salary, take-home pay runs about $52,000 to $54,000 after federal and state taxes — roughly $3,600 a month. Average U.S. rent alone is $1,740 a month, according to RentCafe. Add groceries near $400 a month, student loan payments averaging $434, and utilities around $300, and only about $726 remains — short of the 15% O'Leary recommends.
Even applying 15% to take-home pay instead of gross income — $650 a month, still enough to reach millionaire status by 65 — leaves just $150 a month in discretionary income. The strain shows up in the data: 55% of workers earning $50,000 to $79,999 report feeling behind on retirement savings. The overall personal saving rate sits at just 4.4% of disposable income as of mid-2025, per the Bureau of Labor Statistics, meaning a $68,000 earner is actually saving closer to $3,000 a year, not $10,200.
O'Leary's answer is discipline, not policy. "Don't buy stuff you don't need," he said. "Invest it instead."
The math behind O'Leary's rule is not in dispute — compounding in a low-cost index fund remains the most reliable wealth-building tool available to the ordinary worker, exactly as Buffett has argued for decades. The market has already voted on that question, and it rewards patience over decades, not government promises.
What has changed is the room Americans have to act on it. Rent, groceries, student debt and tax withholding are consuming the paycheck before the 15% ever reaches a brokerage account. That is not a failure of the free-enterprise system that built the S&P 500's returns — it is a symptom of a cost-of-living squeeze that leaves less capital in the hands of the people who actually earn it. The rule works. The problem is what Washington leaves behind for households to invest with in the first place.
