If you are a derivative trader in Indian stock Markets specially an Option writer (Call and put sellers) or futures trader, you must understand various types of margin imposed by your broker. Failing to maintain adequate margin can lead to very high penalty beside ad hoc squaring-off existing positions to trim the size of your overall positions.
The initial margin required for the positions is computed online and on an intraday basis, using a software called SPAN (Standard Portfolio Analysis of Risk). Sellers of options (both call and put) and holders of futures (both long and short), where the potential losses could be high, are required to have sufficient margin in their accounts. The SPAN system uses strike prices, risk-free interest rates, changes in prices of the underlying securities, changes in volatility and time-value to calculate the worst possible move in the security. For the exchanges, SPAN margin covers almost the entire risk for the day, minimizing the systemic risk due to margin pressures.