The TurboTax 100% Accuracy Calculation Guarantee covers any calculation errors caused by the TurboTax software. The guarantee will cover any penalties and interest paid but not any taxes that would have been owed. The guarantee does not cover user entry errors or user errors of omission.
See this TurboTax support FAQ for the Accuracy Guarantee - https://ttlc.intuit.com/questions/2566201-what-is-the-turbotax-100-accurate-calculation-guarantee
