I filed an extension and am finalizing my 2017 taxes. 2017 was my first full year as a sole proprietor with no withholding, I will owe about $1250 in income and SE tax, which is about $300 per quarter.
The issue is that I front loaded the payments, I made timely quarterly payments of: Q1 - $1000; Q2 - $1000; Q3 - $250; Q4 - $250. I figured out as the year progressed that the $1000 quarterly payment was too large and overcorrected in Q3&4 and was short $50-$100 for those payments. The total of the estimated payments was less than my 2016 tax.
I will get a refund but would like to know what to do about the underpayments. Please let me know if it is beneficial to work through Form 2210 or if I should let them calculate a penalty and notify me.
If you overpaid your tax liability and will be getting a refund, there should be no underpayment penalty assessed. Are you seeing any penalty assessed on line 79 of the 1040? I would expect that line to be blank.