If a sale deed has already been executed solely in your mother's name, adding yourself as a co-owner directly to that deed is generally not possible. You may be able to become a co-owner through a gift deed, where your mother gifts you a portion or the whole property. This process requires bank permission, as you are a co-applicant on the loan. If the bank doesn't permit, you might consider switching the loan to another bank. Stamp duty for a gift deed is typically 2% of the gifted portion's value.