Investors closely follow the Sensex. When it rises or falls, it often becomes a quick reference for overall market sentiment. But the SENSEX is more than just a number displayed during trading hours. It represents the performance of 30 large and established companies listed on the BSE. These companies belong to a number of sectors. They include banking, technology, energy, consumer goods, automobiles and pharmaceuticals. This guide explains in detail what Sensex is and how it is calculated.
What is Sensex?
SENSEX stands for Stock Exchange Sensitive Index. It is the benchmark index of the Bombay Stock Exchange (BSE), also known as BSE Ltd.
The index tracks 30 large, liquid and well-established companies listed on the BSE. It was launched in 1986, with 1978–79 as its base period and 100 points as its base value.
The SENSEX uses the free-float market capitalisation methodology. This means companies with a larger value of publicly tradable shares have a greater influence on the index.
The SENSEX is also calculated continuously during market hours. Therefore, its value changes as the prices of its constituent stocks move.
What Does Sensex Represent?
The Sensex provides a broad view of how some of India's largest listed companies are performing.
It can also indicate the general direction of India’s large-cap equity market. When several heavyweight Sensex stocks rise, the index may move higher. Conversely, declines in heavily weighted stocks can pull it down.
However, the Sensex does not represent every company or sector in India. It covers only 30 constituents. Therefore, it should be viewed as a benchmark for large and established companies rather than the entire market.
How Does Sensex Work?
The Sensex is a free-float market capitalisation-weighted index. So, all 30 companies don't have an equal influence on the index.
A company's influence depends largely on its free-float market capitalisation. Put simply, it is the market valuation of the company adjusted for those shares which cannot be easily traded in the market.
For instance, if the share prices of a company included in Sensex increases substantially, then the effect would be more pronounced compared to a similar increase in a smaller Sensex company.
How is Sensex Calculated?
The SENSEX is calculated using the free-float market capitalisation method.
The broad formula is:
SENSEX = (Total Free-Float Market Capitalisation ÷ Index Divisor) × Base Index Value
The calculation can be understood through these steps:
| Step | Calculation | Explanation |
|---|---|---|
| 1 | Share price × outstanding shares | Calculates a company's market capitalisation |
| 2 | Market cap × free-float factor | Calculates free-float market capitalisation |
| 3 | Add free-float market caps | Gives the index's total free-float market capitalisation |
| 4 | Apply the index divisor | Maintains continuity with the base period |
| 5 | Apply the base value | Produces the SENSEX level |
The free-float approach excludes shares that may not normally be available for public trading. These can include certain promoter, government or strategic holdings.
The index divisor also helps maintain continuity after corporate actions, constituent changes and other adjustments.
Example
Suppose a company has a market capitalisation of ₹1,000 crore. If its free-float factor is 0.60, its free-float market capitalisation would be ₹600 crore.
The same process is followed for all 30 constituents. Their free-float market capitalisations are then combined to calculate the index.
How are Sensex Constituents Selected?
Sensex is constituted from the stocks of the BSE 100 universe. Companies must meet specific eligibility and liquidity requirements before they can be considered.
Key criteria include:
- Listing history: A stock generally needs at least six months of listing history on the BSE.
- Trading frequency: It must have traded on every trading day during the six-month reference period.
- Derivative availability: The stock must have a derivative contract.
- Market capitalisation: Companies are evaluated using their market capitalisation.
- Liquidity: Trading activity is considered while selecting constituents.
- Free-float market capitalisation: Companies are ranked based on their float-adjusted market value.
- Sector representation: The selection process considers the representation of different sectors.
- Index committee review: The final additions and exclusions are subject to index committee oversight.
The index is designed to maintain a basket of 30 companies while balancing size, liquidity and market representation.
What Companies are Included in the Sensex?
The Sensex has 30 constituents representing different parts of the Indian economy. The list can change following periodic reviews.
Investors should refer to the latest BSE index information for the current constituent list, as companies can be added or removed during index reviews.
What Factors Affect Sensex?
Several factors can influence SENSEX movements.
Company Performance
Quarterly earnings, revenue growth, profitability and management outlook can affect constituent prices.
Economic Conditions
Inflation, interest rates, economic growth and government policies can influence investor expectations and stock prices.
Global Market Movements
Global equity markets, crude oil prices, geopolitical developments and foreign investor activity can affect Indian equities.
Interest Rates
Changes in interest rates can affect borrowing costs, corporate earnings and investor demand for equities.
Investor Sentiment
Positive or negative sentiment can insist investors to buy or sell shares, influencing the index.
How to Invest in Sensex?
You cannot buy the Sensex directly. It is an index, not a security.
If you want to invest in the companies represented by it, you can consider products that track the index.
The process generally looks like this:
- Open a demat and trading account: Choose a suitable regulated intermediary.
- Select an investment route: Consider a Sensex index fund or ETF.
- Compare available options: Look at expense ratios, tracking differences and, for ETFs, trading liquidity.
- Invest: Purchase fund units through the relevant platform.
- Stay invested: Your investment will generally move with the underlying index, subject to tracking differences and costs.
An index fund is a mutual fund designed to track the Sensex. An ETF also tracks an index but trades on a stock exchange during market hours.
Benefits and Limitations of Tracking Sensex
Benefits
- Simple market indicator: It provides a quick view of large-cap market performance.
- Established companies: Its constituents include several major Indian companies.
- Sector diversification: The index covers multiple industries.
- Useful benchmark: Investors can compare portfolio performance with the index.
- Easy accessibility: SENSEX index funds and ETFs provide ways to obtain index exposure.
Limitations
- Only 30 companies: The SENSEX does not represent the entire Indian equity market.
- Concentration: Heavily weighted companies can have a significant effect on index movements.
- Market risk: The index can decline during periods of market stress.
- Limited representation: Small-cap and many mid-cap companies are not represented.
Conclusion
Sensex is a benchmark index that tracks 30 large and established companies listed on the BSE. It uses free-float market capitalisation to determine the weight of each constituent. Its movements can provide a useful indication of large-cap market sentiment. However, investors should not think of it as a complete picture of the Indian stock market. For investors who want to get exposure to Sensex, they can go for index funds or ETFs. It all depends on individual preferences based on a number of aspects.
FAQs
How does Sensex work?
The Sensex uses free-float market capitalisation to determine the weight of its constituents. Larger companies can therefore have a greater impact on index movements.
Why is Sensex used?
The Sensex is used as a benchmark to track the performance of major Indian companies and as a reference point for investors and market participants.
Why does the Sensex fluctuate?
It fluctuates as the prices of its constituent stocks change. Corporate earnings, interest rates, economic data, global markets and investor sentiment can all influence these movements.
How do I purchase Sensex shares?
You cannot purchase the Sensex itself. You can gain exposure to it through Sensex index funds or ETFs.
What is the difference between Sensex and Nifty?
The Sensex tracks 30 companies on the BSE, while the NIFTY 50 tracks 50 companies on the NSE. Both are major Indian stock market benchmarks.
What is the full form of Sensex?
Sensex is derived from the term Sensitive Index.
How many stocks are in the Sensex?
The Sensex has 30 constituent stocks. The companies included can change following periodic reviews.
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