U.S. stock futures were falling early Tuesday after the S&P 500 closed above 6,000 for the first time in the previous session. The index is on course for its first back-to-back yearly gains of more than 20% for the first time since 1998.

The S&P 500 Index ($SPX) (SPY) today is up +0.21%, the Dow Jones Industrials Index ($DOWI) (DIA) is up +1.02%, and the Nasdaq 100 Index ($IUXX) (QQQ) is down -0.19%. Stocks today are moderately higher,

Most indexes, like the S&P 500 and Nasdaq Composite, assign a higher weighting to the largest companies by market cap. For example, Apple has roughly 11 times the market cap of Coca-Cola, so it has a much higher weighting in the S&P 500. But in the Dow, Apple is the 12th highest-weighted company by market cap because the index is price-weighted.

The ins and outs of membership in the 30-company group that represents success across industries and reflects stock market conditions.

Nvidia joins the DJIA amid cyclical highs, but past trends suggest caution. Find out why NVDA stock may struggle despite the prestigious inclusion.

Shares of Honeywell International Inc. rallied into record territory Tuesday after activist investor Elliott Investment Management L.P. disclosed a large stake and said it was pushing for a breakup of the company.

A breakup of Honeywell's businesses could result in major upside for the blue chip stock over the next two years, the activist investor says.