Short excerpt from a YouTube video by Craig Wear, CFP® giving practical advice on when and how to pay taxes for a Roth conversion. He recommends paying the tax at the time of conversion or via quarterly estimated tax payments, and warns against waiting until April 15 to pay because that can trigger penalties for underpayment.
The deal that you made with the IRS was that when you take that money out, you got to pay tax. So it's probably most recommended to pay the tax at the time you do the conversion. If you are not really on top of your taxes and watching it real closely, you're better off just to pay the tax at the time that you do the conversion. Or you can do it on a quarterly basis through estimated tax payments. Either way works. You just got to make sure that you get the tax in. It's not usually a good idea to wait till April 15 to pay the taxes, because it's very possible that you could have penalties because you didn't get enough paid in at the right time throughout the course of the year.
