An investor sparked a lively debate on Reddit’s r/stocks after asking a simple but heavy question: How can the S&P 500 continue to grow at an average annual rate of 10% for another 30 years?
The user pointed out that if the index maintains that pace, its market cap would double roughly every seven years, ballooning from $52 trillion today to around $900 trillion by 2055.
That number sounded “really stupid and impossible” to the original poster, who noted that with declining birth rates and slowing population growth, the math just didn't add up. “Where is all this money going to come from?” they asked. “Even if we assume inflation wipes out half of that $900 trillion in growth of the S&P 500 in today's money, that's still a ridiculous increase that makes no sense.”
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But many Redditors disagreed or at least explained why it's not as crazy as it sounds. One of the top comments framed it this way: “In 1995 the S&P 500 market cap was ~$3T… Nvidia (NASDAQ:NVDA), Microsoft (NASDAQ:MSFT), and Apple (NASDAQ:AAPL) today are all individually larger than the entire S&P 500 was in 1995. It's unfathomable.”
Several investors pointed out that this kind of growth has happened before and could happen again because of inflation, global expansion and major leaps in productivity.
“S&P500 companies don't only sell in America,” one added. “All the big U.S. companies are just getting started with their globalization,” pointing to China and India and their growing middle class.
Another commenter chimed in: “Half the world’s population lives on $7 a day, so I would say there is room for plenty of growth even if population growth slows down.”
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Other Redditors were more skeptical. For example, one said that population growth, a major tailwind in the past, is slowing down significantly. “Returns will not be what they have been on a market-wide level,” they argued. “Large companies finding increased markets via globalization will not be enough.”
