Here it is. See also my explanation at the end.
(1)
Basic rule for taxpayers not claimed as a tax dependent.
In the case of an individual who
expects to file a tax return for the taxable year in which an initial
determination or renewal of eligibility is being made, and who does not
expect to be claimed as a tax dependent by another taxpayer, the
household consists of the taxpayer and, subject to paragraph (f)(5) of
this section, all persons whom such individual expects to claim as a tax
dependent.
(2)
Basic rule for individuals claimed as a tax dependent.
In the case of an individual who
expects to be claimed as a tax dependent by another taxpayer for the
taxable year in which an initial determination or renewal of eligibility
is being made, the household is the household of the taxpayer claiming
such individual as a tax dependent, except that the household must be
determined in accordance with paragraph (f)(3) of this section in the
case of—
(i)
Individuals other than a spouse or a
biological, adopted, or step child who expect to be claimed as a tax
dependent by another taxpayer;
(ii)
Individuals under the age specified
by the State under paragraph (f)(3)(iv) of this section who expect to be
claimed by one parent as a tax dependent and are living with both
parents but whose parents do not expect to file a joint tax return; and
(iii)
Individuals under the age specified
by the State under paragraph (f)(3)(iv) of this section who expect to be
claimed as a tax dependent by a non-custodial parent. For purposes of
this section—
(A)
A court order or binding separation, divorce, or custody agreement establishing physical custody controls; or
(B)
If there is no such order or
agreement or in the event of a shared custody agreement, the custodial
parent is the parent with whom the child spends most nights.
(3)
Rules for individuals who neither file a tax return nor are claimed as a tax dependent.
In the case of individuals who do not
expect to file a Federal tax return and do not expect to be claimed as a
tax dependent for the taxable year in which an initial determination or
renewal of eligibility is being made, or who are described in paragraph
(f)(2)(i), (f)(2)(ii), or (f)(2)(iii) of this section, the household
consists of the individual and, if living with the individual—
(i)
The individual's spouse;
(ii)
The individual's natural, adopted and step children under the age specified in paragraph (f)(3)(iv) of this section; and
(iii)
In the case of individuals under the
age specified in paragraph (f)(3)(iv) of this section, the individual's
natural, adopted and step parents and natural, adoptive and step
siblings under the age specified in paragraph (f)(3)(iv) of this
section.
(iv)
The age specified in this paragraph is either of the following, as elected by the agency in the State plan—
(B)
Age 19 or, in the case of full-time students, age 21.
https://www.law.cornell.edu/cfr/text/42/435.603#fSo the first bold part say the determination of a dependent is based on the entire Household income, UNLESS that person is NOT a spouse or a child. In the case of a non-spouse, non-child dependent, you follow the rules in paragraph 3.
Paragraph 3 says the income eligibility is based on the
income of that individual alone, unless their spouse and/or children under age 21 live with them, in which case the spouse's and children's income is included.
