@jonpagel the 110% of 2021 taxes is a safe harbor. if you meet this test through withholding only there should be no penalty no matter how much you owe come 4/15/2023.
however, some withholding and some estimates is a different answer
the 4 periods are:
1/1-3/31
1/1-5/31
1/1-8/31
1/1-12/31
for each period, the IRS allows you to use either 1/4 of the total year's withholding or the actual withholding for the period (must use the same method for all columns on 2210)
estimates are only counted for a period if made by the due date for that period which is 15 days after the end of the period or 4/15,6/15, 9/15, 1/15 of the following year. dates are the next business day if the due date falls on a holiday or weekend
an example of form 2210
say that 110% of your 2021 tax is $220K of which you paid $160K through withholding and a $60K estimate in the second quarter
each column of line 10 would be $55K
assume you use even withholding for each quarter then line 11 columns would be $40K, $100K, $40k, 40K
first column line 15 is $40K (line 11)
first column line 17 is $15k (line 10 less line 15) so you have an underpayment for the first quarter.
for the second column
line 12 $0K prior column overpayment)
line 13 $100K withholding and estimate for the quarter
line 14 $15K prior quarter underpayment
line 15 $85K line 13 - line 14
line 16 $0
line 17 not applicable
line 18 (overpayment) $30K line 15 - line 10
for the third column line 18 would show an overpayment of $15K
and the 4th column would show line 18 as $0
thus if you wanted to see if you could eliminate the first quarter penalty you would have to use the annualized installment method. this can be tedious to do because the IRS requires actual amounts not just 1/4, 5/12, 2/3 and 100%
