Why would it include personal income tax? Your tax situation could be different than mine (single vs. married, deductions AKA children, etc.) it would be impossible for the employer to know what you personal income tax is going to be. Insurance? if your spouse has access to a better insurance policy you might opt not to participate in your employers plan so why would they "include" that? Social security and medicare AKA FICA? they pay half, you pay half and the rate is easy to find (7.65%, except this year) 401k? well you are paying yourself there, it's still your money.