Legendary Vanguard Founder Jack Bogle says stocks may well at some point face a “judgment day” that could mean big short term declines, but he’s not advising that investors try to time it.

Bogle tells CNBC that as the Federal Reserve tapers its asset-buying program and raises interest rates, stocks could fall as much as 20 or 25 percent. But he says that stock markets move in “fits and starts,” and trying to time those fits and starts is a recipe for big trouble. He says investors should instead have some money in bonds, as “ballast” against any equity market declines.

Bogle also says corporate earnings are solid and dividends are up 25% since the financial crisis. He thinks corporate America is likely to grow by about 5 percent annually and dividend yields should be about 2 percent, meaning stocks should average gains of about 7% over the long term. That should double an investor’s money (before inflation) over the next decade, he says.