Through 5-18-23, five companies have contributed slightly more than 80% of all S&P 500 gains YTD. The S&P 500 is a market weighted (share price times number of shares) stock index. Apple has provided 26.2%, Microsoft has added 21.8%, NVIDIA has contributed 14.2%, Alphabet another 10.6% and Meta has chipped in with 10.1%, totaling 82.9%.