I'm not sure how additional Federal Income Tax withholding helps with the Medicare Tax unless there is a provision to apply any overage to the Medicare tax -which will probably mean another form.

Maybe it will be clearer to you if you look at the back of the 1040. After income tax and credits against it you come to "Other taxes." All sorts of things in addition to income tax are paid on the 1040. Then you come to payments, where your withholding, regardless of how it was calculated, is credited.

Yes, some calculation method will have to be added. Whether it's a Form, Schedule or worksheet we won't know until the 2013 draft forms are available.

Phil
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