Michael Saylor is at it again. The loudest bitcoin bull in America has predicted that bitcoin will compound at 30% a year for the next two decades, which would turn a $10,000 investment into roughly $1.9 million by 2046.

Do the math with me, because I like math that doesn't care who's talking. At 30% annually, money doubles about every 2.6 years. Start with $10,000 and after 20 years you get 10,000 times 1.3 to the 20th power. That works out to about $1.9 million. Saylor's arithmetic checks out.

The arithmetic is the easy part. The assumption is where I slow down.

I've been watching markets since the late 1980s, and I've heard the 30%-a-year pitch before. Technology funds in 1999. Housing in 2006. Crypto in 2021. Every one of those stories had a charming spokesman with a spreadsheet, and every spreadsheet extrapolated a hot stretch into a permanent law of nature. Nothing compounds at 30% for 20 years. The S&P 500, the best-performing major asset class of the last century, did about 10% a year with real scars along the way.

For bitcoin to hit Saylor's number, it would need to reach a market cap measured in the hundreds of trillions of dollars. That's most of the world's wealth parked in one asset. I don't rule things out entirely, I'm old enough to be humble about predictions, but notice what has to be true for the number to work. When someone shows you a projection, always ask what the world has to look like on the other end of it.

There's also the matter of who's talking. Saylor's company, Strategy, holds an enormous bitcoin position. When a man's balance sheet depends on the answer, his forecast is a sales pitch, whether he means it that way or not. I'm sure he believes it. I believed in a few internet stocks in 1999 too.

My framing is simple. If you have $10,000 you could lose without changing your life, and you want to put 5% of your portfolio into bitcoin as speculation, that's a decision a reasonable adult can make. What you shouldn't do is take a 30% annual return as a planning assumption. Retirement math built on hope has a long history of ending badly, and the people it ends badly for are rarely the ones making television appearances.

The boring alternative: $10,000 in a total market index fund at a historical 8% becomes about $46,000 in 20 years, with dividends reinvested and no requirement that the world rewrite itself. Patience and consistency beat projections, every time I've checked.

But that's just my perspective, not professional financial advice. Do the math yourself, and assume nothing compounds at 30% forever.