I guess I should have looked it up before I replied. Both turbo tax and HR block both said the DD in box 12 is for information only.
https://www.hrblock.com/tax-center/irs/forms/understanding-form-w2-box-12-codes/...
Is your employer contributing to your HSA? There are limits to how much you can put in the HSA since it's pre-tax dollars going in. The max/yr. for families is around $7,500. I'm also self-employed (I get 1099's not W2's) so I don't know if the number you're looking at on your w2 includes...
**I am not a tax accountant** I have no clue what 12c DD is. However, I have a high deductible plan. If you don't have a health savings account, you probably don't have a high deductible plan. If you do, you might want to check to see of they're asking how much you contributed to your health...
1% when they actively held and managed my accounts, now it's discounted to about 0.4% (and shrinking as my assets grow) when I took control of my accounts and use them in a purely advisory role.