Are there any disadvantages to funding a HSA with post-tax dollars (taxable account) as opposed to pre-tax dollars (i.e. payroll deduction)?

My understanding is that you can still use Form 8889 to deduct the amount of your post-tax contribution (up to the total HSA contribution limit for the year) from your income.

How about FICA (OASDI and Medicare) taxes?

  • @Ben Miller: Thanks for pointing me in that direction. It's not exactly the same question as the question is regarding contributing to an existing employer HSA with post-tax funds, but it seems like the answer would be the same with regard to FICA taxes (which are significant enough to dissuade from using said post-tax funds)
    – arcyqwerty
    Oct 26 '15 at 5:31