Was able to enter the correct amount to W-2 Box 12 dd. However, the same amount is duplicated under W-2 Box 12w. How do I eliminate 12w and prevent from happening again?

Hi there, anonymous101.

I'm here to share some about how W2 form boxes work in QuickBooks.

The box 12 is the total of any amounts that fit into a specific category or code. The code DD contains the cost of employer-sponsored health coverage and the code W refers to the contributions to the health savings account. The program will automatically enter the amount in this box based on the items you used on your paychecks.

Please know that there certain health insurance related-items that affect either one or both of these boxes. Please refer to this article to learn more about the supported pay types and deductions in QuickBooks Online Payroll as well as how each impacts federal taxes and forms.

Additionally, you'll want to run the Payroll Details Report for the entire year then make sure that the items used on the paychecks are set up correctly and the correct amounts were used. I'll show you how:
 

1. Select Reports from the sidebar menu.
2. Enter "Payroll Details" in the search bar.
3. Set the appropriate reporting date.
4. Click Run Report.
5. Verify the health insurance items being used and its amount.

I highly recommend visiting this link to know more about how QuickBooks Online payroll populates the boxes on the IRS Form W-2: W2 form boxes explained.

I've also added an article that will guide you in printing your W-2s form.

Do you have other questions in mind? Feel free to leave them below and I'll get back to you as soon as I can.