Thank you very much for your detailed reply to my 3 scenarios, which helped me understand the underlying concept.
Last year I owed a lot more (more than 2x) taxes than I normally do because of an unexpected huge capital gain distribution in late December from a mutual fund, which I have since sold. As a result, TurboTax generated estimated quarterly tax payment amounts that are much higher than necessary for this tax year.
I am now confident that I can recalculate my quarterly payments without owing any underpayment or interest penalty. Thanks again.
