There is a box for the Account Number underneath box 10 in TurboTax on the screen where you enter your 1099-R details.
To access this screen in TurboTax Online you can follow these steps:
- Within your tax return use the magnifying glass icon to search for 1099-R
- Click the Jump to link
- Answer the questions about your 1099-R until you get to the Enter your 1099-R details from XXX screen
- If you already entered your 1099-R you will click Edit for the form you want to add the withholding for then progress through the questions
- Scroll down to the Less common items section and you can see the Account number box underneath box 10