You should calculate your profit as follow

Property Price e.g 800,000
Area e.g 1200 sq.ft
Rate 666 per sq.ft

You paid to the developer approx 100,000 and the price jump from 666 to 700 per sq.ft

Your profit would be 700-666=34*1200=40,800
you have invested : 100,000 and return 40,800