The stock universe for major indices like Nifty 50, Nifty 500, Sensex, etc., is periodically updated by NSE and BSE. This can lead to changes in the stocks included in screeners and backtests, depending on when you run them.

How are index constituents updated?

NSE Indices (e.g., Nifty 50, Nifty 500):

• Reconstituted semi-annually — usually in March and September.
  

• Changes take effect on the last working day of March and September.
  

• More details: NSE Index Rebalancing Schedule.

BSE Indices (e.g., Sensex, BSE 500):

• Typically rebalanced semi-annually — usually in June and December.
  

• Some indices may follow a quarterly review cycle.
  

• Changes become effective typically on July 1 or January 1.
  

More details: BSE Index Media Releases.