I turned 65 in 2018. My company added the value of my unvested retirement benefits (stocks and long-term cash incentives, but not 401K) to Box 5 of my W2 form. This figure was on top of my regular Medicare wages and tips. The result was to spike our federal taxes due. Is this a glitch with TurboTax Premier (which I'm using) or is this supposed to happen: Are our federal income taxes on unvested retirement benefits supposed to be collected at this time?
Items appearing on Schedule 4 are other taxes (including the additional Medicare tax), not income taxes. If you are married filing separately, your employer will not have withheld the entire amount of additional Medicare taxes necessary since an employer only withholds additional Medicare taxes on amounts in box 5 above $200,000 while an MFS filer is subject to additional Medicare taxes when box 5 is above $125,000. Or it's possible that the employer simply failed to withhold the proper amount of additional Medicare taxes since the increase in box 5 came from something other than wages. If Form 5989 line 18 is non-zero, you must pay additional Medicare taxes with your tax return.