After-tax basis rolled over from 401(k) plans needs to be reported as an adjustment to your basis in nondeductible traditional IRA contribution on the first Form 8606 Part I that you are required to file after the rollover. The pre-tax money when rolled over to the traditional IRA remains pre-tax.
Your Forms 1099-R reporting the rollovers from the 401(k)s to your traditional IRAs might have reported the after-tax portion in box 5.
In TurboTax, you report an adjustment to basis by indicating that you made nondeductible traditional IRA contributions, clicking the EasyGuide button, then marking the box to indicate that you rolled over money from an employer plan and entering the amount of after-tax money rolled over to the traditional IRA.
