Let's assume your annual taxable income is $40,000. As a single guy, the first $26,250 is subject to the 15% federal income tax rate, according to the tax code. That's $3,938. The $13,750 remainder "graduates" to the 28% rate, or $3,850. Your total tax then is $7,788 (3,850 + 3,938). Using ballpark figures, if you get paid twice a month, around $324 should be withheld from your check each week for federal tax.But if you just took a flat 28% of $40,000, you'd get $11,200 in taxes, much more than the graduated amount. That's why your bonus check has more money withheld for taxes. It just gets hit with the flat 28%. "Pull out state, city, Social Security, Medicare and 401(k) and that's why it seems like 50% of your bonus disappears," says Jim Seidel, managing editor at RIA, an information provider to tax professionals. Note: 401(k) contributions typically are taken out of bonuses.