About how much of my gross earnings will be taken as tac from the federeal government?

Answer 1

It depends on how much you make, whether or not social securiy and medicare have been withheld from it, your filing status, number of dependents and their ages, and what adjustments, deductions and credits you have. So no way to even give you an estimate, other than to say somewhere between zero and almost 50%.

Answer 2

You can usually count on about 20%