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Capitalization-Weighted Index Definition

What Is a Capitalization-Weighted Index?

A capitalization-weighted index, often known as a market value-weighted index, is a kind of inventory market index during which particular person parts of the index are included in quantities that correspond to their whole market capitalization (shortened as “market cap”).

With the capitalization-weighted methodology, the index parts with the next market cap will obtain the next weighting within the index. Proportionally, the efficiency of firms with a small market cap could have much less of an affect on the efficiency of the general index. Different strategies for computing the worth of inventory market indexes are the price-weighted, fundamental-weighted, and equal-weighted index building strategies.

Key Takeaways

  • A capitalization-weighted index is an index building methodology the place particular person parts are weighted in line with their relative whole market capitalization.
  • The parts with increased market caps carry better share weights within the index. Conversely, the parts with smaller market caps have decrease weightings within the index.
  • Critics of cap-weighted indices argue that the overweighting towards bigger firms provides a distorted view of the market.

Capitalization-Weighted Index

Understanding Capitalization-Weighted Indexes

A inventory market index measures a subset of the inventory market and helps traders evaluate present worth ranges with previous costs with a view to glean details about the present market efficiency. It’s computed utilizing numerous strategies (together with the capitalization-weighted methodology) with the costs of chosen shares.

A capitalization-weighted index makes use of an organization’s market capitalization to find out how a lot affect that individual safety can have on the general index outcomes. Market capitalization is derived from the worth of excellent shares. The funding group can use market capitalization to find out an organization’s measurement, versus utilizing gross sales or whole asset figures.

An organization’s market capitalization is calculated by multiplying its excellent shares by the present worth of a single share. On this means, market capitalization displays the whole market worth of a agency’s excellent shares.

Within the composition of a capitalization-weighted index, massive actions within the worth of shares for the biggest index firms can considerably affect the worth of the general index. Nonetheless, since massive firms with quite a few excellent shares are typically extra secure income producers, they’ll additionally present regular development for the index. Then again, small firms are likely to have a decrease weighting, which might cut back danger if the businesses do not carry out nicely. 

Market-cap indexes present traders with details about all kinds of firms—each massive and small. Many inventory market indexes are capitalization-weighted indexes, together with the S&P 500 Index, the Wilshire 5000 Complete Market Index (TMWX), and the Nasdaq Composite Index (IXIC).

Critics of the capitalization-weighted indexes argue that the overweighting of the biggest firms may give a distorted view of the market. Nonetheless, the biggest firms even have the biggest shareholder bases, which makes a case for having the next weighting within the index.

Calculation of a Capitalization-Weighted Index

To seek out the worth of a capitalization-weighted index, first multiply every element’s market worth by its whole outstanding shares to reach on the whole market worth. The proportion of the inventory’s worth to the general whole market worth of the index parts gives the weighting of the corporate within the index. For instance, think about the next 5 firms:

  • Firm A: 1 million shares excellent, the present worth per share equals $45
  • Firm B: 300,000 shares excellent, the present worth per share equals $125
  • Firm C: 500,000 shares excellent, the present worth per share equals $60
  • Firm D: 1.5 million shares excellent, the present worth per share equals $75
  • Firm E: 1.5 million shares excellent, the present worth per share equals $5

The entire market worth of every firm could be calculated as:

  • Firm A market worth = (1,000,000 x $45) = $45,000,000
  • Firm B market worth = (300,000 x $125) = $37,500,000
  • Firm C market worth = (500,000 x $60) = $30,000,000
  • Firm D market worth = (1,500,000 x $75) = $112,500,000
  • Firm E market worth = (1,500,000 x $5) = $7,500,000

All the market worth of the index parts equals $232.5 million with the next weightings for every firm:

  • Firm A has a weight of 19.4% ($45,000,000 / $232.5 million)
  • Firm B has a weight of 16.1% ($37,500,000 / $232.5 million)
  • Firm C has a weight of 12.9% ($30,000,000 / $232.5 million)
  • Firm D has a weight of 48.4% ($112,500,000 / $232.5 million)
  • Firm E has a weight of three.2% ($7,500,000 / $232.5 million)

Though firms D and E have equal quantities of shares excellent—1,500,000—they symbolize the best and lowest weightings within the index, respectively, due to the consequences of their costs on their particular person market values.

Benefits and Disadvantages of Capitalization-Weighted Indexes

Most of the world’s hottest benchmark indexes are market cap-weighted, making them simply accessible to most traders to realize entry to a well-diversified, broad-based portfolio. Over time, nevertheless, if sure firms develop sufficient, they’ll find yourself making up an extreme quantity of the weighting in an index. It’s because, as an organization grows, index designers are obligated to nominate a better share of the corporate to the index. These firms are typically much less unstable, extra mature, and higher suited to most traders as core holdings. On the identical time, this impact can endanger a diversified index by putting an excessive amount of weight on one particular person inventory’s efficiency because it involves dominate the index make-up.

The Dow Jones Industrial Average (DJIA) is probably essentially the most vital index that isn’t capitalization-weighted. Fairly, it displays the sum of the worth of 1 share of inventory for all of the parts, divided by its proprietary Dow Divisor. Thus, a one-point transfer in any of the element shares will transfer the index by an similar variety of factors.

As well as, index funds and exchange-traded funds purchase further shares of a inventory as its market capitalization will increase or because the share worth will increase. In different phrases, because the inventory worth is rising, these funds buy extra shares on the increased costs; this may be counterintuitive to the investing mantra of shopping for low and promoting excessive.

If an organization’s inventory is essentially overvalued (from a technical evaluation standpoint), the buying of the inventory as its worth (and thus, its market cap) will increase can create a bubble within the inventory’s worth. In consequence, buying shares primarily based on market-cap weightings can result in a inventory market bubble. If the bubble have been to burst, this could ship inventory costs right into a free fall.


  • Capitalization-weighted Indexes mirror the market’s collective opinion of every inventory’s relative worth

  • Giant well-established firms have a better weighting, offering decrease volatility to the index and traders

  • Funds that observe cap-weighted indexes reduce on turnover and the associated buying and selling prices


  • As a inventory worth rises, an organization can have an extreme quantity of the weighting in an index

  • Firms with bigger weightings can have a disproportionate affect on the fund’s efficiency

  • Fund managers can typically add shares of overvalued shares assigning a bigger weighting and create a bubble

Instance of a Capitalization-Weighted Index

The  S&P 500 is a capitalization-weighted index that accommodates among the most well-established firms within the U.S. Here’s a historic actual instance of how the index functioned on a specific buying and selling day:

  • On March 22, 2019, Boeing Co. (BA) closed down -2.83% to $362.17 whereas Microsoft Corp. (MSFT) closed down -2.64% to $117.05 for the day.
  • Boeing had a market cap of $209 billion and a weighting of lower than 1% within the S&P on that day.
  • Microsoft Corp. had a market cap of $909 billion and a weighting of over 3% within the S&P.
  • In consequence, Boeing’s worth decline had a smaller affect on the S&P than Microsoft’s affect regardless that each shares declined by almost the identical share.
  • In different phrases, Microsoft dragged the S&P down extra so than Boeing for that day as a result of Microsoft had a bigger market cap than Boeing.

It is vital to notice that the weightings of the S&P 500 change day by day with the businesses’ excellent shares and their costs, which leads to various impacts on the Index’s total worth.

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