The 1099-R I got from my old employer has a blank for box 2a. How do I know what the taxable amount should be? Do I figure that out or will turbotax do it for me?
Its ok if your Form 1099-R box 2a is blank. It's quite common for that box to be left blank.
You should enter your Form 1099-R exactly as you have received it. TurboTax will determine how much of your distribution is taxable based on your 1099-R entries and your answers to the follow-up questions in the interview process.