There's an algorithm used when calculating how much tax someone should pay. If you were to look at an actual tax chart, you could see the progression/exponential rise of tax to income ratio.
Basically, the more you make, the more they take from you. Sometimes if you're not married and don't have any dependants, and can't itemize your deductions, it doesn't pay to make more money. If you make over say $60k, and are single without kids, you really start paying alot more taxes, it goes into another tax bracket. You always should mark single and zero on your w4 form for your job, to make sure you don't have to pay out/get a return. If you end up owing after claiming single and zero, then you need to add extra money on the w4 form to be taken out of your paycheck.
