Cite? My husband’s prior employer didn’t offer either, as far as he knew (then again, he wasn’t in their health insurance because mine was better and cheaper). I admit I could be wrong about it being mandatory, of course.
That’s a separate thing, however, from the health insurance premium the OP was asking about.
The flex spending is also better than planning on deducting your out-of-pocket, for the same “must itemize, only amounts over 7.5%” rules. The danger being, of course, that you overwithhold and wind up losing the money at the end of the year.
I understand that your box 1 and 3 would differ by the D. pretax 401(k), but why would it differ by taxable insurance premiums? I’d think those amounts would be included in box 1 taxable income and perhaps noted in Box 14.
Insurance premiums are not always taxable. Section 125 cafeteria health plans are specifically set up so that the premiums are withheld pretax, and the amount of the premiums is not taxable income.
See here for an explanation. The wikipedia article links to the IRS website, but the IRS explanation is a lot harder to follow.