Properly calculating personal taxes

Question

When taking into account how much Federal/State income taxes, FICA and MED have to be removed from your income, do you calculate that based off of your Gross or AGI?

Answer 1

For Federal, it's the taxable income as answered in How to base my income tax bracket?

State has a similar process, but each state is different. e.g. some states do not honor IRA deductions, and some states permit a deduction for the 529 college savings account which Federal does not.

FICA and Med come off the very top of income with a couple exceptions - FICA has an income limit, in 2012, it's withheld only up to $110,100 of income. And - I believe certain deductions such as FSA (The "Flexible savings account" for medical expenses) may be pre-FICA deductions.

Edit - in case my wording was ambiguous - With the small exception of the FSA deduction, FICA/Med is calculated on one's gross income. FICA/Med does not reduce one's taxable income for Federal or state income tax.

Answer 2

Federal income tax is based on adjusted income (post-tax-exempt-deductions). State income taxes vary by state. Social Security is based on gross income, but has a ceiling (in the low 6 figures) above which no additional taxes are withheld, while Medicare taxes are a flat tax with no ceiling.