Why do I have a $16 underpayment penalty added on to my tax return? When was this estimated?

[jeffcnsusand]

How was the $16 estimated?

[AndreaC1]

If you didn't pay enough tax throughout the year, either through withholding or by making estimated tax payments, you may have to pay a penalty for underpayment of estimated tax. And the underpayment penalty may be imposed if you owe more than $1,000 in tax for the current year. TurboTax automatically fills out Form 2210 (the form used to calculate the penalty) for you if it’s determined that you didn't pay sufficient income tax during the tax year.

More details on this penalty can be found on the IRS’s website here Topic No. 306 Penalty for Underpayment of Estimated Tax

Once you print a full copy of your return, you can look for Form 2210 and you'll find the calculations for the underpayment penalty there. 

You can also find more details on how to possibly eliminate that penalty here below:

https://ttlc.intuit.com/replies/4242891