Ltcg on transfer of property

Hello,

I have a question on Long Term Capital Gain of my property.

I had booked an under construction property in 2012 and I had taken the Bank loan for disbursements to the builder. The bank had made the payments to the builder over a period of 5 years (till 2017).

Now the property is ready to move in. However, I have now decided not to take over the property from the builder, as I am transferring the ownership of my property to someone else.

I have paid 90% of the value of the property to the builder till now and rest will be settled between the new buyer, builder and myself via a agreements.

I do have some capital gain due to the transfer.

My question is how do I calculate the long term capital gain, in this kind of scenario.

Any help is highly appreciated.

Thank you. Pradeep