What Happens When the Stocks in an Index Change?

Cosmit Paniat
3 min readFeb 14


When a stock is added or deleted from an index, there are several things that happen. Some of them can be very important, while others are more minor. Indexes regularly rebalance to keep their selection relevant to the underlying description and account for corporate actions. These changes are generally expected to positively impact the price behavior of the included stocks.

Index providers update their indexes on a regular basis, adding or removing securities or changing the weighting of existing index constituents. This process helps maintain a high level of index liquidity and consistency in the underlying asset class. It also allows investors to adjust their portfolios better to match their investment goals and risk tolerance levels. This is called rebalancing.

Rebalancing is a strategy that involves buying and selling mutual funds, ETFs or other investments to bring a portfolio back in line with its original asset allocation. For example, if an investor had originally allocated 60% stocks and 30% bonds, they might need to sell 5% of their stock holdings to purchase bonds.

Index rebalances are publicized events that are announced well before the implementation date. PEs view these as opportunities to create value for their clients by using projections provided by the index provider to build portfolio solutions for each rebalance.

When the stocks in an index change, it can significantly impact the index’s value. Stocks are added to or removed from an index when companies merge, grow or shrink and when individual stocks make significant changes in their price. As a result, the stocks in an index must be periodically rebalanced. This helps to keep the overall value of an index consistent.

One way to ensure that the stocks in an index are rebalanced is by using a divisor. This is a number chosen at the beginning of a price-weighted index and applied to bring the seemingly random sum of the individual shares of each constituent down to a more manageable index value.

The Dow Jones Industrial Average (DJIA) uses a divisor to keep the total value of its 30 stocks in line with market conditions. The divisor is adjusted regularly to account for small events that would otherwise affect the index. These adjustments include issuing new stocks in the index, dividends and stock splits.

Stocks are weighted in an index according to various factors, including price or market capitalization. These weights affect how the stocks in an index perform and may affect your overall portfolio.

One common type of index is the price-weighted index (PWI). It is calculated by dividing the individual stocks’ stock prices by the total index value. Another is the capitalization-weighted index (CWI). It is a type of index that weights the stocks by their relative total market cap, with larger companies carrying more percentage weights in the index.

Critics of this method argue that overweighting larger companies gives a distorted view of the market and can distort the overall performance of the market. Regardless of the type of index you use, remember that weights change over time and should be rebalanced regularly. This is especially true for equal-weighted and fundamental-weighted indices.

Market capitalization measures how valuable a company is in terms of its stock value. It can be used as a guide for investors to assess the risk of investing in a specific company and how much it could return over time. A company’s market capitalization is calculated by multiplying its share price times the number of outstanding shares it has. The calculation can include common shares, preferred shares and treasury shares.

There are many advantages to having a large market cap, including access to investor capital and economies of scale. However, these advantages can come with downsides, such as slower growth rates and a higher risk of failure. A company’s market cap can fluctuate, which can significantly impact its share price. Market capitalization can also be affected by stock splits or special dividends.



Cosmit Paniat

Cosmin Panait is a New York-based investment fund manager who has backed both private and public enterprises.