Assuming that your wife had been the owner (not beneficiary of) of both IRAs inherited by your daughter, just like your wife's basis applied to all of her traditional IRAs in aggregate while she was alive, your wife's basis applies to these inherited IRAs in aggregate. One is not permitted to allocate the basis to just one of these accounts in isolation for the purpose of Form 8606. For the pro rata calculation on Form 8606, the combined value of these IRAs must be present on line 6 and the combined gross amount of the distributions from the two IRAs must be on line 7. The resulting taxable amount should then be divided proportionately between the two Forms 1099-R so that the total taxable amount that TurboTax places in the two boxes 2a equals the total taxable amount shown on line 15c of the Form 8606.
