my formula is for the default calculation and assumes no withholding.
If you have withholding, the combined amount of witholding plus estimated tax should be 25%
You may also use Form 2210 Schedule AI but that's at filing time, after the fact, and much more complicated, so so it is hard to calculate quarter by quarter in advance,
Confusion is what happens when you break up your question into two or more threads.
@mellynlee
