The S&P 500 gained about 1.2 percent to close at 2,104.05, above 2,100 for the first time since Aug. 17. The Dow Jones industrial average added 165 points to end at 17,828.76, positive for the year so far. The Nasdaq composite outperformed to close at 5,127, while the Nasdaq 100 hit highs last seen during the dotcom bubble of March 2000.
Lance Roberts, head of Streettalklive.com, said Monday's trade was "first day of the month repositioning."
"We could be down a little tomorrow because we had a good day today, but we're right in the middle of resistance, which is becoming support," he said, noting stocks could have a good finish to the year, after a slight pullback around Thanksgiving or early December.
Read More Stocks could fade after best month in four years