What if I pay 100% (110%) of my actual 2018 taxes as the estimated tax during 2019, and still owe more tax at the end of 2019? Is there a penalty?

[DDollar · Accepted solution]

No.  If you pay 100% (110% - depending on your income) of your 2018 tax as either estimated tax or payroll withholding, and you still owe when you file your tax return, there is no penalty for underpayment of estimated tax, as long as the additional amount owed is paid by April 15.

[mnv1234]

I too paid 110% of my actual 2018 taxes in the April 15 2018 estimated tax payment (and no other payment the rest of the year), but I am still being assessed an underpayment penalty by TurboTax for 2018 taxes.  Why is there still a penalty?