The query is: " I am buying an under construction house for investment. i indend to sell it as soon as I get a good price. I booked it last year 2011 will get the registration done in 2012 and might get the possession in 2013/14. I want to know from when will capital gains be calculated. Date of booking, registration or possession."
As seen from the facts you have stated, you will be considered to have acquired the property only on the date of registration of the Sale Deed in your favour. Normally, it will be also the date on which you are put in possession of the property.
You will not get the benefit of S 2(47)(v) of the Income tax Act / s 53A of the Transfer of Property Act, as you have neither paid the whole consideration, nor have been put in possession of the property.