After waiting on hold for well over an hour with HSA Bank, I got the exact same answer from them - "We can't tell you what to put on the form. You have to consult a tax person." Yet here in this community thread, the tax experts are saying that the HSA custodian is the only one who CAN figure it out for you and they do that at the time the excess contribution is distributed. My inclination is to leave that box blank because my copious research on this topic has not yielded a clear answer. The HSA Bank phone representative told me that it is okay to leave the box blank, but who knows what the person who processes the form will think of that.
