<prompt> Human: My wife and I were self employed, doing gig work, from Jan 1 2017 until about mid August. During this time, we were on a low earnings trajectory such to not have the requirement to file federal quarterly estimated tax: we expected to owe less than 1,000 in tax for 2017. I actually attempted to electronically, when filing pay the April 15 first quarterly payment just to be on the safe side, but for some reason that was not my fault it didnt go through, and IRS sent me a note later saying so. I then did not pay any other quarterly payments, federal or state was also under that states threshold.Then in mid August, my wife started a new job--and stopped her self-employed gig work. I continued mine. Her new job pays a good salary, starting near the end of September, so we will likely owe more than 1,000 in taxes for all of 2017, due now to her Sep-Dec earnings from this job. Therefore, it seems perhaps we should have paid estimated quarterly tax payments. I just didnt know at the time she was going to get this job.What should we do now to avoid, if possible, any possible underpayment of taxes penalties?  <response>: First, if you dont make 4 equal quarterly payments each quarter is evaluated independently for underwithholding. And, any tax withholding from your w-2 income is treated for this evaluation as though it was received on January 1. So the easiest route would to be to increase your wifes withholding to cover your entire tax bill or at least within 1k.If that isnt possible for whatever reason, then make an estimated payment asap. That will help minimize your overall lateness for the year and thus any underwithholding penalties. 