Add dividends to the S&P 500's price rise and the total return for investors is 13.8 percent — the most in 15 years.
"We're not surprised at the positive performance across U.S. equity markets this year because the fundamentals of the economy are improving," says Steve Rees, head of U.S. Equity Strategy for JPMorgan Private Bank. "We were surprised, though, at how quickly we achieved that performance at the start of the year."
Here are the five best first halves for the S&P 500 since World War II. Data before 1957, when the S&P 500 was launched, combine the values for four earlier S&P indices: the industrials, utilities, financials and transportation:
— 1975. First half: up 41.7 percent. Second half: down 3.2 percent.
The 1970s began with a bull run, but things soon went sour. The oil crisis of 1973-1974 caused oil prices to soar and the economy entered into what would be a 16-month recession in November 1973. The annual rate of inflation began to climb. It surged as high as 12.2 percent in November 1974 from 3.4 percent a year earlier. The S&P 500 dropped 48 percent between Jan. 11, 1973 and Oct. 4, 1974.
The market soared in the first half of 1975 as inflation moderated and investors grew hopeful the economy was pulling out of its slump. The market gave up some of its gain in the second half of the year as doubts about the strength of the economic recovery grew and concern rose that inflation might re-emerge. New York City's fiscal crisis also weighed on markets.
— 1987. First half: up 27.4 percent. Second half: down 17.4 percent.
In early 1987, investors were still enjoying a bull run that had begun in August 1982. Unemployment and inflation had fallen. Tax cuts and low interest rates had spawned an economic boom.
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But things unraveled in a big way.
Stocks peaked on August 25, when the S&P 500 closed at a record 336. Rising interest rates and concerns about a stock bubble prompted a sell-off in October. That culminated in 'Black Monday' on Oct. 19, 1987, when the index plunged 57 points, or 20.5 percent, to 224.
— 1983. First half: up 22.2 percent. Second half: up 0.25 percent.
In early 1983, the great '80s bull run was just beginning. It had started the previous summer after the Fed lowered its benchmark interest rate from 14.5 percent to 10 percent. President Reagan's tax cuts also got the economy going after it had contracted for much of 1982.
But the surge in stocks stalled in the second half. Investors worried that the expanding economy would revive inflation and compel the Fed to raise rates.
—1986. First half: up 20.7 percent. Second half: down 1.8 percent.
The factors that had given stocks a lift in 1983 were still in play. Also, falling oil prices helped lower the threat of inflation and allowed the Fed to cut interest rates. The price of oil dropped as low as $10.42 a barrel in March, after starting the year at $26.30 a barrel.
— 1954. First half: up 20.6 percent. Second half: up 26.2 percent.
The stock market was on its longest bull run, from 1949 to 1961. In 1954, an improving economy and rising confidence after the Korean War helped stocks. By November, the market had finally returned to its peak before the Wall Street Crash of 1929.