Registered domestic partners must still, however, file their federal tax returns as single individuals. California income tax returns rely on the federal adjusted gross income (AGI) from federal tax returns, so registered domestic partners must use an alternative method for calculating their AGI.
Registered domestic partners still need to file their federal tax returns as single individuals. California's income tax system depends on the federal adjusted gross income (AGI) from these returns; thus, registered domestic partners have to use an alternative method for calculating their AGI.