Cost of Aquisition of flat

1) Usually sale deeds are registered on the basis of the guidance value (set by the local authorities) that is also used for the purpose of payment of stamp duty.

2) Total payments (usually made against agreement to sell) will be regarded as the cost of acquisition

3) Stamp duty and registration charges paid can be claimed as a deduction u/s 80C subject to the limit of Rs.1.5 lacs

You may claim stamp duty that has actually been paid. In the above case, this will be computed on the basis of value as per sale deed.