In California, most of the benefits are the same, but there are a few significant differences:
In order for a domestic partnership to be issued, the members must share a common residence. This is not required in order to marry.
Both partners must be 18 years old or older, whereas in a marriage it is possible to receive an underage marriage license.
A man and a woman may also receive a confidential marriage license, which is not on public record and requires no witnesses, whereas domestic partners can’t obtain a confidential license.
Domestic partnership rights are not portable from state to state within the United States, as marriages are.
Domestic partnership is not a federal benefit, so couples cannot apply for green card status for the non-citizen partner as married couples can. Domestic partnerships do not carry any kind of status that would allow a U.S citizen to marry another citizen into the U.S.
A domestic partner is not automatically considered the parent of a child the other partner gives birth to or adopts, as is the case with marriage.
Domestic partners can only inherit if there is a will or wills stipulating that each partner should inherit the other’s property. In this case, they are subject to taxes that a marriage-based inheritance is not subjected to.