If the taxable amount is truly incorrect by that much, it's going to be due to an entry error. Look at the individual lines of the Form 1040 Worksheet to see which particular line shows a taxable amount that is too low. In particular, check line 4b where the taxable amount of the IRA distributions will be. If that line is too low, check the Forms 1099-R that you have entered. Be sure to click the Continue button on the page that lists the Forms 1099-R that you have entered and verify all of the information that TurboTax asks you to provide.
