Suppose I choose to make pre-tax payroll contributions to my 401(k) and/or HSA, of an amount that takes up most of my paycheck. I also selected on my W-4 form to make an extra tax withholding per paycheck, of an amount that also takes up most of my paycheck. Obviously, both of these cannot be satisfied at the same time. Which one takes precedence?
Is it going to make as much of the payroll contributions as possible, and tax is only going to be withheld from the remaining amount, even if they don't withhold as much extra taxes as I told them to? Or, will they reduce payroll contributions to such an amount that it would be possible to withhold extra taxes to the amount I chose?