The Federal Reserve’s implicit patience in deciding when to begin lifting interest rates is raising the odds for the Standard & Poor’s 500 Index to hit 2,600 this year, according to Yardeni Research Inc.

There is now a 30 percent chance that the S&P 500 will reach that level in an “irrational exuberance scenario,” up from 20 percent, according to Edward Yardeni, the president and founder of the research firm. His “rational exuberance scenario” remains at 60 percent with a target of 2,150.

“If the fundamentals do improve, all the better,” Yardeni wrote in a note to clients today. “If not, then repeat: They can count on the central banks to provide yet another round of ultra-easy money, which will send stock prices still higher. We will probably have occasion to repeat our appreciation again and again before the end of the current bull market.”

Global stocks rallied Wednesday, with the S&P 500 jumping 1.2 percent, after the Fed said higher interest rates in April are unlikely and it won’t tighten until it is “reasonably confident” inflation will return to its target and the labor market improves further. Policy makers also lowered their median estimate for the federal funds rate for the next two years and cut their assessment of the economy.

24 Percent

Yardeni’s most optimistic forecast represents a 24 percent increase in the S&P 500 from yesterday’s close. On average, Wall Street strategists predict the benchmark gauge will end the year at 2,237.

Sentiment toward U.S. stocks is far from irrational exuberance. The percentage of global money managers who are underweight American equities is the highest since 2008, a survey by Bank of America Corp. showed earlier this week. A net 35 percent of respondents in the survey picked the U.S. as the worst place to invest in the next 12 months, the most in almost a decade.

U.S. stocks trail virtually every developed market in 2015 as accommodative central-bank policy from Europe to Japan lifts global equities and the Fed winds down programs that helped the S&P 500 triple since 2009. After beating global stocks every year since 2009, the S&P 500 was up less than 2 percent in 2015 through yesterday, compared with an almost 3 percent advance in the MSCI World ex-USA Index.

“Yesterday’s FOMC statement deleted the word ‘patient’ regarding the Fed’s rate-hiking plans. Yet the tone of the statement suggests that the FOMC remains very patient, and is in no rush to raise rates,” Yardeni said. “The melt-up in global stock markets can proceed.”