When a stock enters the Nifty 50, every fund that tracks the index has to buy it, and every fund has to sell the stock that leaves. On 29 September 2026, the last day before BSE replaced Wipro, Wipro traded 164,453,787 shares on the NSE, 15.6 times its average for the previous five sessions. BSE traded 7.5 times its average.
This guide covers how NSE Indices decides on a change, why the trading clusters on one day, and what that day looked like for BSE and Wipro. It is a description of how the index works and of what already happened, not a view on either stock.
Who decides, and how often
The Nifty 50 is run by NSE Indices, the index arm of the NSE. According to Bajaj AMC's summary of the methodology, the index is reviewed twice a year, using average data for the six months ending 31 January and 31 July. Changes are announced with four weeks' notice before they take effect, which in practice means the end of March and the end of September.
The key measure is free-float market capitalisation: the market value of the shares that are actually available to trade, leaving out promoter and other locked-in holdings. A company with a large promoter stake can be big in total value but small in free float, and it is the free float that counts.
Weights inside the index are also based on free-float market capitalisation, so the largest free-float companies count for the most.
The 1.5 times rule
A stock outside the index doesn't get in just by being bigger than the smallest member. To protect the index from constant churn, an eligible stock's average free-float market cap has to be at least 1.5 times that of the smallest constituent it would replace.
The September 2026 review shows the rule working in both directions, using the six-month averages reported by Angel One and Ventura Securities:
| Company | Six-month average free-float market cap | Outcome |
|---|---|---|
| BSE | ₹1,40,879 crore | Included |
| Wipro | ₹55,930 crore | Excluded |
| TVS Motor Company | ₹84,566 crore | Not included |
| Divi's Laboratories | ₹82,930 crore | Not included |
The arithmetic for BSE is simple: ₹1,40,879 crore divided by ₹55,930 crore is about 2.52, well over 1.5. TVS Motor and Divi's were both larger than Wipro, but once Wipro was out, they had to clear 1.5 times the next-smallest constituents, and they didn't. That's why one review produced one swap, even though two more companies were bigger than the stock that left.
Ventura Securities reported that the same review made 27 additions and 27 removals in the broader Nifty 500, so a Nifty 50 change is usually the most visible part of a much larger rebalance.
Why the trading lands on one day
An index fund or ETF that tracks the Nifty 50 aims to hold the same 50 stocks in the same weights. It is judged on tracking error, how far its returns drift from the index. If it buys the new stock a week early or a week late, its holdings differ from the index for that week.
The cleanest way to match the index is to trade at the same price the index uses on the day the change takes effect. For the September 2026 change, BSE joined from 30 September, with the change effective after the close on 29 September, as Angel One reported from the NSE Indices announcement. So the natural moment for tracking funds to buy BSE and sell Wipro was the close on 29 September.
That close is set by an auction. Since August 2026, stocks in the F&O segment have their official closing price fixed in a closing auction rather than from the last 30 minutes of trading, which I explained in the closing auction guide. Large orders that need the official closing price can go into that auction.
I haven't found a sourced estimate of how much money tracks the Nifty 50 or how many shares funds needed to trade on 29 September, so I won't guess one. The volume data shows the effect directly.
What 29 September looked like
These are daily figures for the two stocks on the NSE, from Zerodha Kite market data. The five-day average covers 22 to 28 September.
| BSE | Wipro | |
|---|---|---|
| Shares traded, 29 September | 30,101,047 | 164,453,787 |
| Average shares traded, previous five sessions | 4,011,088 | 10,525,356 |
| Multiple of the five-day average | 7.5× | 15.6× |
| Close on 29 September | ₹3,200.00 | ₹156.79 |
| Change from 28 September | +3.31% | −2.95% |
| Where it closed in the day's range | At the day's high | At the day's low |
Both stocks traded far more than usual, and both closed at the extreme of the day's range in the direction of the index trade: BSE at its high, Wipro at its low.
The next day, 30 September, the first day of the new index, both moves partly reversed. BSE fell 3.38% to ₹3,092.00 and Wipro rose 1.09% to ₹158.50. On 6 October, BSE closed at ₹3,305.00 and Wipro at ₹161.84 (today's market report).
This is one change, on one day. It shows the shape of an index-change close, but I wouldn't build anything on a sample of one swap, and the moves on the days around it had other news in them too.
What changes for the stocks afterwards
Joining the Nifty 50 changes who holds a stock, not what the company earns. In practice:
- More passive ownership. Index funds, ETFs and index-linked products hold the stock for as long as it stays in the index. The leaving stock loses that ownership, though Wipro remains a large company with its own investors and other index memberships.
- Index weight follows free float. BSE entered with a weight based on its free-float market cap, so it is a small part of the index rather than an equal one-fiftieth.
- Derivatives follow the index. Nifty 50 futures and options now reflect BSE's moves, in proportion to its weight, and no longer reflect Wipro's.
Before the change, the two stocks had been moving in different directions. Ventura Securities reported that, in 2026 up to 10 August, BSE shares had risen 37% and Wipro's had fallen 29.5%. That divergence is what moved their free-float values far enough apart to trigger the swap at the July review.
How to track the next change
The next scheduled review uses data for the six months to 31 January 2027, with changes due to take effect at the end of March. If you want to follow it:
- Watch for the NSE Indices press release, usually published a few weeks after the cut-off date.
- Note the effective date and the last trading day before it. That close is where index-tracking trades are concentrated.
- Compare that day's volume with the stock's recent average, as in the table above. Kite's historical data or NSE's bhavcopy files both have daily volume.
For context on where the index opens and closes on any given day, the GIFT Nifty guide and the pre-open session guide cover the other end of the session.
Sources
- Nifty 50 review schedule, six-month averages and four weeks' notice: Bajaj AMC, Nifty 50 rebalancing
- BSE replacing Wipro, free-float figures, the 1.5 times rule, TVS Motor and Divi's: Angel One, Ventura Securities
- Nifty 500 changes and 2026 share price moves to 10 August: Ventura Securities
- Daily prices and volumes for BSE and Wipro, 22 September to 6 October 2026: Zerodha Kite market data (NSE)
This guide is for information only. It is not investment advice or a recommendation to buy or sell any security. I am not registered with SEBI as an investment adviser or research analyst.