According to SEBI recommendations, the NSE has decided to enhance the Margin Period of Risk (MPOR) in the Equity Derivatives market from one day to two days starting January 21, 2019.

As volatility over two days is considered instead of one, the SPAN +Exposure margin will increase by a maximum of 41% of the present margins. Nifty and Banknifty futures margins will rise by almost Rs 10,000 and Rs 7,000, respectively.
A more extensive description of how the change will impact SPAN+Exposure margins can be found below:
SPAN margins are charged to cover the worst-case scenario for the contract you're trading on a given day. The exchange has now updated this to account for potential volatility over the next two days. The Price Scan Range of the index or stock is used to calculate SPAN margins.
The worst potential fluctuation in a scrip in a day is the Price Scan Range (PSR). The PSR is calculated using the scrip's daily volatility. For index contracts, the daily volatility is 3 sigma, and for stocks, it is 3.5 sigma. If the 3(and 3.5) standard deviation is less than the above-mentioned minimum, the exchange mandates a minimum PSR of 5% of the contract value for indexes and 7.5 percent for stocks. This will now be multiplied by 1.41 to account for price fluctuation over two days.
Over and above SPAN margins, exposure margins are levied. For index F&O, this is 3% of the contract value, and for stock F&O, it is 5% (or 1.5 sigma, whichever is larger). This will be raised to 4.24 percent for the index and 7.07 percent (or 1.5 sigma, whichever is larger) for stock F&O.

The Short Option Minimum (SOM) is a margin requirement for all strikes of option short contracts that are outside of the Price Scan Range. Nifty, for example, has a PSR of 762 points (covering a 7 percent movement). This practically means that owning a 11700 CE or 10000 PE is risk-free, but such contracts are subject to a 3% SOM. This will now be increased to 5% of the contract value. For stock options, there is no growth in SOM.