The max pain theory says that the underlying tends to drift towards the strike where option buyers collectively lose the most, which is also where option writers pay out the least. It is a theory and not a rule, and the index often expires away from the max pain level.

For each strike, the calculator takes every call strike below it and every put strike above it, multiplies the distance in points by the open interest at that strike and adds everything up. The strike with the lowest total is the max pain strike.

No. Max pain is only one of many factors, and its usefulness is debated. News, global markets, fund flows and hedging can move the index far from the max pain strike, so do not use it on its own for trading decisions.

PCR (put call ratio) is the total put open interest divided by the total call open interest for the selected expiry. A higher value means more put open interest than call open interest. It is one of several sentiment indicators and should be read together with price action.

The straddle method uses the sum of the at-the-money call and put prices as the market's expected range around the spot price. The implied volatility method multiplies the spot price by the at-the-money implied volatility and the square root of the time left to expiry in years.

The open interest and option prices come from the OPIFY option chain feed. The 'as on' time shown above the results tells you when the data was last updated. Outside market hours you will see the last available data.