If the Form 1099-R has code 4 in box 7 and the IRA/SEP/SIMPLE box is marked, the distribution is from an inherited traditional IRA. (TurboTax should be able to figure this out on its own, but doesn't.) If the IRA/SEP/SIMPLE box is marked but there is some other code is in box 7, the distribution is from your own IRA , not from an inherited IRA.
