Dear Minnu ,as our friends said this applies to all ticket booked online and it applies to all airline,reason for increased fare even return sector is becoz PNR usually once created for a single booking,CANNOT be cancelled one sector ,because it will affect whole booking and so you will be affected by any fare diff. becoz by the time try to confirm seat on diff.date other than original date then for sure not easy to get same fare,especially PEAK TIME otherwise go as per your original plan,no charges will apply simple...