Code DD is only information to you to tell you how much your employer spend for health coverage - you do nothing with it.
Code D is the amount of salary deferrals to a 401(k) plan. You do nothing with than either other than enter it on the W-2 screen in box 12 just like it is on the paper W-2.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
