@Opus 17 wrote:
IRS tax letter requesting $319 penalty for 2019 taxes. paid in full $13,540 July 10. 2018
If that is true, then you owed a substantial penalty for 2017 both for being late and for under-paying throughout 2017 to end up that far behind. In that case, Turbotax might have offered to calculate the penalty for you, but it is only an estimate, because only the IRS calculation of penalties is deemed correct. If the IRS is now asking for an additional penalty and interest amount because the amount calculated by Turbotax in July, 2018, was not high enough, that situation is not covered by the accuracy guarantee.
This would still be true if "2018" is a typo and you really meant that you paid $13,540 on July 10, 2019. The tax system is supposed to be pay-as-you-go, and if you owed that much at the end of the year, it means you under-paid during the year. Whether or not Turbotax calculated a penalty and included it in your tax bill, the IRS gets the final say.
However, if this is the first time you have owed a penalty, you can ask for a one-time abatement (relief). (Interest can't be abated, but it may be reduced when it is recalculated without the penalty.)
https://www.irs.gov/businesses/small-businesses-self-employed/penalty-relief-due-to-first-time-penal...
