What does it mean if your name is on someone else's bank account? It depends.
For all deposit accounts, the rights of the parties to a multiple party account are determined under the Pennsylvania Multiple-Party Account Act. A joint account is one that is payable on request to one or more parties whether or not any mention is made of survivorship. If you and your mother have a joint account, and either one of you may write checks on the account or make withdrawals from the account, this is a joint account. Who can write checks and make withdrawals is determined by the deposit agreement with the bank or other financial institution. How your names appear on a statement or on checks is not determinative. The rights of the parties are determined by what is in the account agreement.
Who owns a joint account during the lifetime of the joint parties? According to the Multiple-Party Account Act, a joint account belongs to the parties in proportion to the net contributions of each party to the deposit unless there is clear and convincing evidence of a differing intent. Example: you and Mom have a joint account. All of the funds in the account were deposited from Mom's earnings. During the lifetimes of you and your mother, the money in the account belongs to your mother. Note that the bank is not going to keep track of whose money is in the account. The bank may pay the whole of the account to either one of you in accordance with its deposit agreement. If you make a withdrawal or write a check to yourself, it is either a gift to you or you owe a debt to your Mother.
On the death of one party, the joint account belongs to the surviving joint owner or owners unless there is "clear and convincing evidence of a different intent at the time the account is created." For example, if you and Mom have a joint account and Mom dies, unless there is clear and convincing evidence to the contrary, the account belongs to you on Mom's death.
There are many arguments over accounts that are made joint for "convenience." If Mom puts your name on a bank account as a joint owner so that it is easy for you to write checks for her to pay her bills, but she does not intend that the account pass to you on her death, that is what is referred to as a convenience account. The account is in joint names only for convenience, not because it was intended to pass to the check-writer by right of survivorship on Mom's death. Unfortunately, after Mom is deceased; it is very hard to determine what her intention was, especially if the surviving joint owner asserts that Mom intended the ownership of the account to pass to the survivor. The statute presumes that the account passes to the surviving joint owner. It is up to the other claimants to prove that Mom had a different intention, proven by clear and convincing evidence.
Because of the many problems of proof and the opportunity for heirs and beneficiaries to argue, I never recommend convenience accounts. It is far better to use a power of attorney. Then there is no confusion as to who owns the funds.
For Pennsylvania inheritance tax, on the death of a co-owner of a joint account or any joint property, the taxable estate of the co-owner includes a fraction of the value of the property. The fraction is one divided by the number of co-tenants. For example, if three brothers are joint owners of an account, on the death of one of them, one-third of the value of the account is subject to Pennsylvania inheritance tax. Whose funds were contributed to the account are irrelevant for this purpose.
Joint accounts created within one-year of death are taxable as they would have been before the joint account was created. For example, if Mom adds your name to an account as a joint owner and then dies six months later, the whole value of the account is subject to inheritance tax, not just one-half.
For Pennsylvania inheritance tax, joint property is taxable even if the decedent's name was added only for convenience. Assume Mother and Daughter are joint owners of an account and one of them dies. One-half of the value of the account is subject to inheritance tax at the death of the first to die. It is important to note that even if all the money belonged to Mother, if Daughter dies first, Mother will have to pay inheritance tax on half of the value of the account. This is one of many reasons why joint property as an alternative to making a will is not such a good idea. This puts Mother in the position of having to pay inheritance tax to get her own money back. The only time this does not apply is if a child predeceases a parent before the child exceeds age 21.