You always owe the correct tax you owe. Turbotax pledges to cover an penalties and interest if Turbotax makes a mistake that results in penalties. If you got an IRS letter and want to verify their calculations are correct before paying, you will need to download and install Turbotax 2017 on your own computer, get your 2017 data file, and prepare an amended return.
Amending instructions are here.
Amend <a rel="nofollow" target="_blank" href="
https://ttlc.intuit.com/replies/3288565">https://ttlc.intuit.com/replies/3288565</a>
The accuracy guarantee claim form is here. However, in the past, Turbotax has blamed this on user error. I can't prove one way or the other, but I suspect that is not right since the problem only occurred in 2016 and 2017 that I know of. If Turbotax denies your guarantee submission, you can also request a penalty abatement from the IRS if this is the first time you have owed a penalty. (The interest can't be waived, though.)
Accuracy guarantee
<a rel="nofollow" target="_blank" href="
https://ttlc.intuit.com/replies/4202723">https://ttlc.intuit.com/replies/4202723</a>
Abatement
<a rel="nofollow" target="_blank" href="
https://www.irs.gov/businesses/small-businesses-self-employed/penalty-relief-due-to-first-time-penal...>
If you caught this mistake on your own, file the amended return and pay only the tax you owe, don't accept Turbotax's offer to calculate any late fees. Wait for the IRS to bill you, then you can submit an abatement request or an accuracy guarantee claim.
