By the end of trade, the benchmark index is set to have gone 3,453 days without a fall of 20% or more, marking the longest rally ever in US history.
The positive run stems from the 9 March 2009, when the world was reeling from the financial crisis.
Overall the index has risen almost 325% in the period, lifted by companies such as Apple, Microsoft and Amazon.
This year, the gains have sometimes been shaken by worries about rising inflation, interest rates and trade disputes.
Still, the S&P 500 – the broadest measure of the US market – remains up more than 6% so far this year.
It closed at 2,862.96 on Tuesday, within striking distance of the record high of 2,872.87 it hit on 26 January.
That performance, which has coincided with broader economic growth, outstrips global markets.
“The bottom line is that the US is doing well – and much better than any other market,” said Howard Silverblatt, senior index analyst at the S&P Dow Jones Indices.
The US has Silicon Valley to thank for much of this rally – dubbed a bull market, which is loosely defined as a rally that consistently avoids a 20% decline.
Apple has been the single biggest contributor to the S&P index, accounting for 4.1% of the gains since 9 March 2009, followed by Microsoft.
Overall, technology companies contributed more than 22%, followed by the consumer discretionary sector – a category that includes Amazon – at about 16%.
This year, the tech sector has been responsible for more than half of the rise on the index.
This has fueled some concerns about a tech bubble.
But Sam Stovall, chief investment strategist at CFRA Research, said the frenzy that accompanied previous market rallies has been largely absent.
In April 2007, about 65% of Americans had money invested in the stock market, according to Gallup. That share had shrunk to about 55% this year.
“Investors were hurt so badly by the prior bear market that they have been very mistrustful,” Mr. Stovall said, noting the current run has been dubbed the “most hated” bull market.
“I don’t think we’re getting that kind of irrational exuberance.”
Behind the gains
The US government and central bank took extraordinary action in 2008 and 2009 to spark the recovery, investing billions to bail out struggling banks and car companies and buy up securities backed by troubled home loans.
As jobs returned, consumer spending – the main driver of the US economy – picked up. Global expansion provided another boost.
While many analysts forecast the slow and steady economic rebound – the stock market gains, especially in the US, have been surprisingly strong, said John Rekenthaler, vice president of research at Morningstar.
He said that’s in part because US companies have largely avoided passing higher profits onto employees in the form of higher wages, keeping inflation in check and interest rates low.
They have also lifted share prices by purchasing their own stock and benefited from loose enforcement of competition rules.
Last year, the US slashed its corporate tax rate from 35% to 21%, further helping the corporate bottom line.
“Employees wouldn’t be sharing so much in higher revenues,” Mr. Rekenthaler said. “Shareholders win and non-shareholders lose.”
Gains aside, the returns of the current bull market have been lackluster compared to prior rallies, said Mr. Silverblatt.
Since 9 March 2009, the S&P index has risen at an annual rate of about 16.5% – compared to an average of more than 22% in prior expansions.
The index’s roughly 325% returns fall short of the 417% gain during the previous record-setting bull market, which ran for most of the 1990s.
“You’re not going to cry for either one, but the bottom line is the other one did better,” Mr. Silverblatt said.
Analysts said the steadier returns may signal that the current bull market remains sustainable – at least over the next 12 months or so – assuming that factors like inflation and interest rates remain on their current trajectory.
“It’s not the most lucrative but I don’t know that I would say I’m dissatisfied,” Mr. Rekenthaler said. “It’s got a more stable feel to it.”