Taxes are complicated and simple answers are usually not possible. You can use this tool to do an estimate https://turbotax.intuit.com/tax-tools/calculators/taxcaster/?s=1.
That said; assuming
you have a tax liability, claiming another dependent would save you $4050 (a
dependent’s exemption) times your marginal tax bracket (e.g. $4050 x 15% =
$608)*.
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). There is no income limit for a QC but there is an age limit and/or
student status, a relationship test and residence test. Only a QC qualifies a
taxpayer for the Earned Income. They are interrelated but the rules are
different for each.
Since your sister is not full time student,
over 18, she cannot be a QC. 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 (sister
qualifies) OR live with the taxpayer ALL year
2. His/her gross taxable income for the year must be less than $4,050 (2016)
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
*If your sister also
qualifies you for Head of Household filing status, that would result in
additional tax savings.
