For the purpose of preparing Form 8606, TurboTax knows nothing about your year-end balance in traditional IRAs unless you enter the value. It's common for users to inadvertently miss entering the year-end balance when they've made a distribution from a traditional IRA and they have basis in nondeductible contributions, resulting in an incorrect Form 8606. I first suggested to TurboTax Product Quality somewhere around 2014 that when Part I of Form 8606 shows a distribution that TurboTax require a non-blank line 6, even if the correct value is zero. Nothing has been done to implement this error-check in TurboTax, so the problem persists.
