"What is my household income?"
That depends on who is asking.
First, as others have mentioned, if three people live together (grandmother, mother, and child), the grandmother can't file as head of household unless the grandmother claims the child as a dependent. HOH does not just mean "head of the family," it is a special tax status for single parents and people in a similar situation who pay most of the household expenses and claim a child dependent. The only time it is possible for one person to claim a child for the child tax credit and a different person to claim the child as a qualifying person for HOH ("splitting" the tax benefits of the child) is when the two people are the biological parents who are divorced or separated and living apart.
Now, the definition of "household income" depends on who is asking. For some state tax credits (like the New York State Household Credit) it is all the taxpayers who live in the household. Are you asking for a federal tax reason like the ACA insurance subsidy, or are you asking about a state tax credit or deduction?
