The table below shows the historical weightings of Apple, Microsoft and ExxonMobil in S&P 500 index for the past 10 years. At the end of September 2015, the weights of these largest components were 3.69%, 1.93% and 1.82%. Check the full dataset of index weighs from here.
Weights of the largest S&P 500 companies
|Exxon Mobil Corp.||3.47%||3.92%||5.03%||3.25%||3.20%||3.60%||3.06%||2.69%||2.13%||1.82%|
Purchase historical weights of the current S&P 500 companies between 3/31/2005 and 9/30/2015. The index weights are listed for the last day of each quarter.
The largest components of S&P 500
The weight of Apple reached its peak during the autumn of 2012 when the company made almost 5% of the index. During the next year the weight of the IT giant quickly halved but started to rise again during the summer of 2014 and is now clearly the number one component.
ExxonMobil used to dominate the whole index but the company’s importance has been steadily decreasing since January 2009. Lately the decreasing oil price has made investors to worry about the company’s earnings.
The weighting of Microsoft has been quite steady during the past decade, fluctuating near 2%. The company overtook ExxonMobil as the second largest component during the third quarter of 2015.
The impact of one component to the index price
When the price of Apple is rising or falling, what is its impact to the index price? Calculating the effect is simple if you know the component’s weight. For example, on March 31st 2015 Apple made up 3.91% of the index. If the stock price of the corporation increased by 5% during this day and the prices of all the other components stayed the same, the value of the index would have risen 0.0391 * 0.05= 0.196%.