Nifty 50 vs Sensex: what an index is, and how NSE and BSE build theirs

What a stock market index is

A stock market index is a recipe written in advance. It says which stocks are in the basket, how much of each the basket holds, and when the list is reviewed. The index level is the value of that basket today against its value on a base date, scaled to a round starting number.

When a newsreader says "the market fell 1% today", they almost always mean one index fell 1%. The index is a shorthand. It does three jobs:

• A thermometer. It tells you, in one number, what large Indian companies did today.
• A benchmark. Fund managers, PMS providers and rules based strategies are measured against it. SEBI requires mutual funds to show their returns next to a benchmark index.
• Something to hold. Index funds and ETFs buy the same stocks in the same weights, so investors can own the recipe.

The recipe matters more than people expect. Change the weights and the same 50 companies give a very different result, which is the subject of the direct indexing guide and the beat the Nifty guide. The free indices and benchmarks module covers the theory with a quiz.

NSE and BSE, the two exchanges behind the two indices

India has two main stock exchanges. BSE, in Mumbai, is the older: it traces its history to 1875. NSE was set up in the early 1990s and began screen based equity trading in November 1994, which moved most trading from the trading ring to terminals. Most large companies are listed on both, and the price of a share on one is almost always within a few paise of the other because traders close any gap.

Today NSE handles most of the cash market. Reports of exchange data in 2025 put NSE above 90% of cash equity turnover, and BSE at about 7%. For a long term investor buying delivery shares this hardly matters: your broker routes the order, the shares land in the same demat, and the price is the same. The exchange matters more for derivatives, which is where the two indices are used most heavily.

1. Jan 1986BSE launches the Sensex

   30 stocks, base year 1978 to 79 set at 100.

2. Nov 1994NSE starts screen based equity trading

   Orders matched on terminals across the country.

3. Apr 1996NSE launches the Nifty 50

   50 stocks, base date 3 Nov 1995 set at 1,000.

4. Sep 2003The Sensex moves to free float weights

   Only shares available to trade count towards a company's weight.

5. Sep 2025Expiry days swap

   Nifty weekly options move to Tuesday on NSE, Sensex options to Thursday on BSE.

How the Nifty 50 is built

The Nifty 50 is run by NSE Indices. Its rules, from the factsheet and methodology, in plain words:

1. Universe. Companies listed on NSE that are eligible for trading in the futures and options segment, so they are large and liquid.
2. Selection. The 50 largest by free float market capitalisation that pass the liquidity and listing history tests.
3. Weight. Each company's weight is its free float market value divided by the total. A company whose promoters hold most of the shares counts only the part that trades.
4. Review. Twice a year, with cut off dates of 31 January and 31 July. Changes take effect at the end of March and September.

On 30 Sep 2026 the index held 50 stocks, and financial services made up 37.45% of it. One bank alone was 10.38%. That is what market cap weighting does: the largest companies drive the number.

How the Sensex is built

The Sensex is run by Asia Index, a BSE company. Its recipe is close to the Nifty's, with three differences you can see:

• 30 stocks, not 50. The Sensex picks 30 large, liquid companies listed on BSE.
• An older base. The base year is 1978 to 79, at 100. That is why the Sensex number is roughly three times the Nifty number; the levels mean nothing on their own.
• Review in June and December, twice a year like the Nifty, on its own calendar.

Like the Nifty, the Sensex weights by free float market value, and it has done so since September 2003. Because the 30 Sensex companies are almost all among the largest Nifty 50 companies, the two indices hold mostly the same money in the same names.

Nifty 50 vs Sensex, side by side

Why they move almost together, and when they do not

Over a day, a month or a year the two indices usually move within a fraction of a percent of each other. The reason is overlap: the largest banks, the largest energy, IT and telecom names are in both, and in both they carry the most weight. The 20 extra companies in the Nifty are smaller and add less.

They drift apart when the extra 20 Nifty names have a very different stretch from the 30 shared ones, or when one index adds a company before the other. Over long periods the gap has been small. If you are choosing between a Nifty 50 fund and a Sensex fund, the cost of the fund and how closely it tracks its index will matter more than which index it tracks. The tracking error calculator shows how to measure the second.

What the index return does not tell you

A few traps catch new investors:

• Price index or total return index. The level you see on the news is the price index. It ignores dividends. The total return index (TRI) adds them back. Over the five years to 30 Sep 2026 the Nifty 50 TRI returned 6.38% a year against 5.13% for the price index; that gap is the dividends.
• Points are not percent. A 500 point move in the Sensex is a smaller percentage than a 500 point move in the Nifty, because the Sensex level is higher.
• The index is not the market. The Nifty 50 is 50 companies. NSE's Nifty Total Market index had 755 constituents on 30 Sep 2026. Mid and small companies can have a very different year, which the large, mid and small cap guide covers.

How to invest in the Nifty 50 or the Sensex

You cannot buy an index itself. There are three ways to hold what it holds:

• An index fund. A mutual fund that buys the index stocks in index weights. You buy units at the end of day NAV, through SIPs if you like. Cost: the fund's expense ratio.
• An ETF. The same basket as a fund unit that trades on the exchange through the day, in your demat. Cost: the expense ratio plus brokerage and the bid and ask spread.
• The stocks themselves. Buy the constituents in your own demat. With 50 names this needs enough money to buy whole shares near their weights, and a rule for keeping up with the twice yearly changes.

The third route is what direct indexing means, and it lets you change the recipe: equal weights instead of market cap weights, for example. The index investing page explains the method.

How this shows up in RupeeCase

Nifty 50 Equal Weight holds the same 50 Nifty companies stock by stock in your own demat, but gives each the same 2% instead of the market cap weight, rebalanced every 4 weeks. That removes the top heavy tilt in the donut above. Its model CAGR is 16.35% with a deepest fall of −15.71%, as of 27 Apr 2026, with a minimum of ₹2,49,000 as of 8 Aug 2026. Every RupeeCase strategy page draws its model curve against the Nifty 50 TRI on the same chart. The blog note the Nifty 50 is 10 stocks plus 40 footnotes shows what the weighting choice did on our own record.

Questions investors ask