The IRS asks that after-tax basis rolled over from the 401(k) be reported when Form 8606 is required for some other reason. The basis rolled over from the 401(k) is reported as an adjustment to the basis in nondeductible traditional IRA contributions. In TurboTax this is done by clicking the EasyGuide button after telling TurboTax that you made nondeductible contributions to your traditional IRAs, then marking the box indicating that you rolled money over from an employer plan and entering the amount of after-tax money rolled over.
