Last year I sold some of the RSUs I got from my employment. I got both a form 1099-B and a "Supplemental Information" form, showing me the adjusted cost basis for the sale. The company managing the funds for our company told us that we had to complete a form 8949 to be sure that we weren't paying the taxes twice (on vesting, some shares were withheld to pay the tax and the proceeds and withholding were reported on my W-2).
The problem is, the minute I enter the "Adjustement codes" into the Turbo Tax 8949 form, my taxes go up! What am I doing wrong?
I'm not sure why you are entering adjustment codes. What you should do is enter the Form 1099-B in TurboTax as it is stated, and then adjust the cost basis reported on it as is necessary to reflect the vesting income listed on your W-2 form. It sounds like you have the correct cost basis numbers, so you just need to enter them after you enter the Form 1099-B.
On the stock sale screen, indicate that the cost basis is missing or incorrect and you will have an opportunity to enter the correct cost basis: