I-864 Affidavit of Support (FAQs) (state.gov)
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How do I calculate my household size?
The Form I-864 asks for the financial sponsor’s household size. When calculating their household size, sponsors must include:
Their spouse,
Any children by birth, marriage, or adoption living in the sponsor's residence,
Anyone else claimed as a dependent on the sponsor's tax return for the most recent year, regardless of whether they are related to the sponsor or have the same principal address as the sponsor,
The principal visa applicant,
Any derivative applicants who plan to immigrate within six months,
Any other people in the United States whom the sponsor is supporting on a different Form I-864, if the obligation has not terminated, and
Any nondependent siblings, parents, or adult children who reside in the sponsor's household who are not dependents, if they complete a Form I-864A.
A sponsor does not have to include people on other I-864s who have not yet immigrated to the United States.