Q. Why are my contributions, to a 401k plan, subject to FICA tax, but my employer's contributions are not?
A. Just because that's the way the law was written.
Q. Are the employer 401k contributions "non taxable employee benefits"?
A. Not really. They are free of FICA tax. But, they are only tax "deferred" benefits, for income tax purposes. When it comes time to withdraw that money (take a "distribution"), the amount distributed will be subject to income tax at "ordinary" income tax rates. You will not get the more favorable long term capital gains/qualified dividends tax treatment. In addition, if you withdraw the money early (without a qualified exception) you will be subject to a 10% penalty.
Q. When the IRS says "Employer contributions", is that only the amount my employer matches, or is it what I contribute PLUS my employer's match that we do together through payroll deduction?
A. It's only the employer share. But your pre (income) tax share will also be subject to income tax on distribution.
