Property resale - which date is considered as sale date

Hi,

I have a query for property Resale Date for tax and indexation calculation purpose.. For example:

A. 1 Jan 11 - Getting into agreement with buyer for Sale with Token amount Signing agreement on stamp paper

B.  1 Mar 11 - Signing Sale agreement with 40% payement

C. 1 Apr 11 - Complete payment and Registration of property by buyer

Question is : From the above three dates which date should be used for tax calcuation (which year tax should be paid) and indexation. Agreement happened in one FY and Registration happened in next FY.

Regards,

Neeraj