In California, as in many states, parents are free to give their child whatever last name they choose, including the mother's surname, father's surname or a completely different surname altogether. If an unmarried woman gives birth, she is free to make this decision by herself. However, she cannot designate a person as the child's father on the birth certificate until paternity is established.
California, like all states, recognizes both legal and physical custody. A parent with physical custody provides a home for her child; if she also has legal custody, she has the authority to make important decisions for her child, such as decisions regarding healthcare, education and religion. Either form of custody may be sole, or held by one parent only, or shared by both parents.
When an unmarried woman gives birth to a child, she automatically has both physical and legal custody of the child. Until paternity is established, she enjoys sole legal custody, which means she is the only one with authority under California law to name her child. Thus, she may choose any last name she likes. She can give the child her last name, the father's last name, or any last name she wants. However, she cannot add the name of her child's father to the birth certificate until paternity is established, usually through a voluntary declaration of paternity signed by both parents or by a court action.
If a child is born to a mother who is married at the time of the birth, her husband is presumed to be the child's father under California law. As such, he shares both physical and legal custody of the child with his wife, unless there is a court order to the contrary. As a result, he and his wife have equal rights to name their child, including choosing the child's last name. Medical personnel will likely presume the parents want to give the child the father's surname, but the parents are free to give the child any last name they choose.
Last Name Changes
If one or both parents wish to change a child's last name after her birth, but before the child turns 18, they may do so by submitting a petition for name change to their local court. A hearing on the matter is held, after which the judge will approve the name change if it is in the best interests of the child. If the name change request is due to a clerical error, parents can usually have the name corrected by submitting an amendment request to the California Department of Public Health.