Dear Querist,
On the facts given, this should be treated as LTCG, as your rights in the flat arose from booking/allotment/Builder Buyer Agreement in 2012-13/2013, not from registration in 2026.
Since sale value is ₹56 lakh, buyer has to deduct TDS @ 1%, i.e. ₹56,000.
Exact indexed cost cannot be finalised without date-wise payment details , but stamp duty/registration charges can be added to cost. Based on your facts, tax may be nil or very low under indexed LTCG calculation.
Keep allotment letter, BBA, payment receipts, RERA orders and registry papers ready for final computation before sale/ITR filing.
For a more detailed review of your case, you may book a phone consultation.
CA Shubham Goyal