Yes, annualizing is a PITA, since you need to go thru your income records and break everything down by Qtr, even while your year-end tax forms don't show any kind of breakdown. It's painful enough, that if the penalty is small, I don't bother for any penalty under ~$50 (but that's my personal pain limit ).
The issue with including the Estimated payments along with the withholding, for exceeding a certain % level to eliminate the penalty. That really depends on whether all the Estimated payments were exactly the same $$ amount, or were uneven. For example: the first 3 payments being $500 each, and the last one being a $million (and getting a huge refund ), that may in total go over the 90/100/110% limit, but unless you run the full annualized income calcs, one may still be considered to have underpaid the first 3 qtrs.....since all income is considered to be gained evenly until you annualize to indicate exactly when each $$ was received.
((((AND....I have absolutely no idea how the allowed delayed estimated payments, and quarterly estimates are properly to be dealt with, along with the 2020 income quarterly annualizations.....is it all a first half together, and the last 2 qtrs separately..... or what?....that's a muck-up for doing the 2020 annualizations....maybe someone else knows far better than I do))))
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
