Long term gains.. practical question

zanis 0071 (68 Points)

23 October 2021  
If 3 people brought land together at rs.880500 in 2015-16
And gave for development in 18-19
Sale taken place in 21-22 for rs.1920000 what will be capital gains for 1 person who sold his ?

My view..
Cost of acq will be 880500/3=293500
Indexed cost = 293500*317/254=366297
Sale= 1920000
Sale - indexed cost= 1553702
Long term gains = 1553702 x 20%=Rs..310740

Some people say that there will be cost when you gave for land development(rule statement in deed) where builder calculates his marketvalue and you need to take the proportionate sft for ur land..and it will form part of your cost..is this a valid form to do?can anyone explain this?do we need to take that cost also?