Additional Medicare Tax withholding kicks in at $200K not $250K. But thanks for trying to explain the tax withholding code to me. If you are married then you deal with it on your joint return when you file your personal income taxes which are no concern to the employer. You seem to think that you can add on every tax imaginable to come up with a federal effective income tax rate. I hope you don't do your own income tax returns and are paying over 40% to the IRS. If you are you really should consult a tax advisor. Have a nice evening.