Happy Birthday, Warren!

The legendary Warren Buffett turns 94 next month — Aug. 30 to be exact. And as is frequently the case when he turns a year older, investors wonder what a post-Buffett Berkshire Hathaway will look like. That’s especially true this year, with Buffett’s longtime partner Charlie Munger having passed away last year and CEO-designate Greg Abel waiting in the wings.

I’m a Berkshire investor myself, and I don’t plan to go anywhere when Buffett is no longer part of the show. If you are a Berkshire shareholder, you might want to keep your powder dry as well.

Why? For one thing, Greg Abel seems unlikely to mess up the formula. And — ironically — because Berkshire’s days as a marvelous investment seem to be over, its astounding long-term record under Buffett notwithstanding. In many ways, Berkshire has become more like an index fund than a conventional corporation.

So it’s not as if something magical will depart when Buffett does.

According to Berkshire’s most recent annual report, the stock returned 4,384,748% to its investors from the time Buffett took control in 1965 through the end of last year. That’s 140 times the 31,223% return for the S&P 500 (^GSPC), the standard market benchmark.

But that was then, and this is now.

As I’ll show you, recent Berkshire investors — including my wife and me — haven’t done remotely as well relative to the rest of the market as Buffett and his early followers have done.

A little background is in order.

For most of my career, I didn't own Berkshire because I was an employee of publications that frequently wrote about Buffett. So I never bought any shares during Berkshire’s salad days, much as I wanted to.

But on Jan. 7, 2016, the first week that I became self-employed, my wife and I made a modest purchase of Berkshire stock in our joint brokerage account and have held it ever since.

And guess what? The huge long-term advantage that Berkshire shows compared with the S&P 500 has totally disappeared since our purchase. In fact, we’d have been a bit better off buying an S&P 500 index fund than buying Berkshire.

From our purchase date through last Monday, Berkshire was up a respectable 214%. That was also its total return because it didn’t pay any dividends during that period. However, during that same period, Admiral-class shares of Vanguard’s S&P 500 index fund returned 232%, including reinvested dividends, according to calculations that Jeff DeMaso, editor of the Independent Vanguard Adviser, did for me.

In other words, my wife and I got into Berkshire when its stock market glory days had passed.