There are bulls, and then there's Jeremy Siegel.

On Tuesday's episode of "Futures Now," the Wharton finance professor didn't just argue that stocks are cheap. He proclaimed that the Dow Jones industrial average will rise to his "fair market value" estimation of 18,000—10 percent above current levels—as companies continue to perform better and better.

"It could get there by the year-end, it could get there sooner, it might be later," Siegel said. "But I certainly don't think that we're in the ninth inning of the bull market yet."

In fact, it's not even time for the seventh inning stretch.

"I'm a bull, and I can't believe what S&P is putting out for earnings estimates in 2014," he said. "Operating earnings 2013 over 2012 were up 10.6 percent; S&P reported earnings were up 16 percent from last year. They're expecting reported earnings to be up 20 percent this year. We didn't have a real good economy last year, and we got 16 percent earnings growth.

"If any of these earnings estimates pan out—and they are bullish—hey, we're in about the fourth or fifth inning of this bull market," Siegel added. "This could be ... much more than 18,000 on the Dow.

"It is remarkable how firms have been able to churn out the dollars despite GDP growth last year, as we know, of really 2.5 percent," he said.

Siegel, the author of "Stocks for the Long Run," the 1994 classic in its 5th edition, is also bullish in the short term.

(Read more: Siegel: I'm a bull, but these two things worry me)

"The market had been at that high of 1,850, 1,858," he said. "It could not get over it, and it broke through late last week. And that ... the short run—right now, a move of 5 or 10 percent certainly can be there."

Siegel's fair market value estimate for the is 2,000.

—By CNBC's Alex Rosenberg. Follow him on Twitter: @CNBCAlex.

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