Ltcg on sale of of under construction flat

Cost of acquisition will be the allotment price plus the other construction linked payment made to acquiring the property. Payments other than allotment price is also payment / expenses incurred toward acquiring the property, hence it will be part of cost of acquisition. Since the flat has been sold even before possessing the flat, the allotment letter date shall be the year of indexation for cost of acquisition. But as the flat is still under-construction and construction linked payment is pending, you will have to enter into a tripartite agreement , you, the buyer and the builder. 

Thanks Mihir

Please advise the full allotment price has not yet been paid as two installments are pending so we have to tka elallotment price as cost only.

Further can you support any case law for the same

Yes, whatever has been actually paid, will become cost of acquisition. Of course, not paying the full price will affect the sale consideration. I don't have a caselaw, but you can search in google with "under-construction sale LTCG" I think you can get similar cases, if not exact, over the internet. 

But cant we take full allotment price

Cost of acquisition is on actuals.

Thanks Mihir

What if i first payoff the full price to builder by taking advance fro someone and then sell the same

Then the payment made toward allotment price plus other payments, if any, shall become your cost of acquisition.