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.
Even though they are registered domestic partners, they must still file their federal tax returns individually. Since California’s income taxes are based on the federal adjusted gross income (AGI), registered domestic partners need to find a different way to calculate their AGI.