The proper way to report these is not to zero out the tax in 2b, but to take a credit on the tax return for income "re-sourced by treaty".
This is done in the Foreign Tax Credit (Form 1116) section of TurboTax. This requires completing the UK tax return first, to determine the amount of the tax credit that is eligible to be taken on the US tax return for the income. If the UK return is complete, you can enter the amount of the income that was taxed as well as the tax paid in this section.
If it isn't yet complete, you may wish to file an extension to extend the due date of the return until after the tax information is available.
For more information about filing the Form 1116 in TurboTax see Claiming the Foreign Tax Credit. For information on how to file an extension, see How do I file an IRA tax extension.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
