Can I claim my 70 yr old mother who lives with me, even though she has already filed

[tiffersbippy]

She only collects social security

[MaryM428]

If your mother qualifies as your dependent, then you can claim her.  But she would have to file her return and indicate that someone else can claim her as a dependent.

To find out if you do qualify to claim here go through this IRS Interactive Tax Assistant - Who Can I Claim as a Dependent?

If she filed her return and checked that she is not a dependent, then you claim her as a dependent and efile, the efile will be rejected.  She would need to amend her return and check the box that someone else can claim her as a dependent.  You would need to print and mail your income tax return and include a letter to the IRS about claiming your mother as a dependent after she already filed.  

Your mother would be a qualifying relative if she meets the qualifications.

[Hal_Al]

There are two types of dependents, "Qualifying Children"(QC) and standard ("Qualifying Relative" in IRS parlance even though they don't have to actually be related).  A person can still be a Qualifying relative dependent, if not a Qualifying Child, if he meets the 6 tests for claiming a dependent:

1. Closely Related OR live with the taxpayer ALL year
2. His/her gross taxable income for the year must be less than $4300 (2020).
3. The taxpayer must have provided more than 1/2 his support

In either case:

4. He must be a US citizen or resident of the US, Canada or Mexico
5. He must not file a joint return with his spouse or be claiming a dependent of his own
6. He must not be the qualifying child of another taxpayer

Nontaxable Social security doesn't count as income, for the income test, but social security money she spends on her self does count as support not provided by you, for the support test. Money she puts into savings & investment does not count as support she spent on herself. Note that a parent is closely related so there is no requirement that she live with you at any time, during the year. But if you provided a home it helps your support case, unless they own the home you live in. If no one person (or married couple) provides 50% of the support (for example your siblings are also sending support), then a "multiple support agreement” (IRS Form 2120) can be used, to allow you to claim the dependent. https://www.irs.gov/pub/irs-pdf/f2120.pdf

The IRS has a worksheet that can be used to help with the support calculation. See: http://apps.irs.gov/app/vita/content/globalmedia/teacher/worksheet_for_determining_support_4012.pdf The support value of a home is the fair market rental value, divided by the number of occupants.