Option writing

On 19/12/2014 suppose I short NIFTY8300 PE (exp-29/01/2015),premium is Rs.139/=(previous close is Rs.169/=),provided I have cash balnce Rs.20000 for margin blocking,(one lot)

1.How much amount will be credited to my account?

Say,if Rs.169x25=Rs4225 is credited to my account can I use it for trading on

19/12/2014(FRIDAY).

1. What will happen to the extra credit,ie ((169x25=4225)-(139*25=3475)) Rs.750/=

Aasuming you are talking about shorting at 169 premium.

169 x 25 = 4225 will be credited to your account, which you can use for further trading on Friday itself.

But your account will be blocked around 20000 as margin.

If you get profits like premium moved close to 139, then your contract is already in profit of rs 30x25=750 which will show as your MTM profit in your positions window.

This profit 750 will not be credited to your account.

You can only get the profits if you square off. So until that this MTM value change into more profits or even losses what you incur.

So only when you are squaring off, your profits are credited and your entire 20000 margin is credited back.

If you are in losses, the losses will be subtracted from your margin and remaining margin will be credited to you.

Also remember, when you square off at 139, you need to pay the premium so 139x25 will be taken from your margin and remaining amount will be credited to you.

1. When you short an option, you get the premium credit based on the price you short your options. So if shorted at 139, you get a credit of 139 x 25 = Rs 3475 is credited to your trading account.

2. The premium credited to your account can be used for trading on the next day onwards. The reason for this is because all F&O settlement happens on T+1 day basis.

@TKS
Yeah,like Nithin said, if you use the premium credit on friday itself, some penalty 0.5% or so may be levied for the excess money you used to trade (other than what you had in the morning as account balance)
If you use he premium credit on Monday, no penalties.