the rapid rise of a few already massive tech stocks this year is causing nasdaq to make unusual adjustments to its popular growth index the company announced on july 7 that it will do a special rebalance of the nasdaq 100 index  which will take effect before the market opens on july 24 the company said a special rebalance can be used to address overconcentration in the index by redistributing the weights while the index is already rebalanced on quarterly basis nasdaq tries to keep the five biggest stocks below a 40 combined weighting in one rebalance per year designated as the annual adjustment according to the firms methodology the five biggest stocks appear to be over that threshold currently according to the holdings of the invesco qqq etf  which tracks the index