For your basket order to be placed you must maintain the required margin, but when the orders are executed the final margin will be blocked from your trading account.

The final margin is not a separate margin that is to be brought in, it is the same amount that will be blocked out of the required margin after execution.

Here is an example:

Suppose you place a basket of options spread in nifty options of BUY NIFTY SEP 15500 CE and SELL NIFTY15700 CE

You have to maintain the required margin of 1,20,104.55/- to place the order but when the order is executed 29,422.05/- will be blocked.

The final margin in an options spread basket order:

When you short/write an option as an option seller you receive the premium, this premium is debited and the final margin is ascertained.

Taking the previous example:

The required margin to place short order without spread is 2,05,943.80/-

Since we have created a spread basket order the margin requirement for the short order is 19,354/-

The premium received here is 90,682/-, which can be seen on the buy order window.

Hence we arrive at the final margin of 29,422.05/- which is the required margin - premium (1,20,104.55 - 90,682.50)

Note:

1. To avail of margin benefit, please go through this article on how to place a basket order.
2. It is necessary to have the required margin to place the basket order because even though the final margin is blocked if one of the legs is squared off, the margin will increase substantially and will bring risk.