maybe wrong. withholding is considered paid equally for each quarter for underpayment penalty purposes or you can elect to use the date(s) actually withheld. but estimated tax payments are deemed paid on the date specified if done online or the postmark date if done through the mail.
but whether you are subject to underpayment penalties for not paying in enough is subject to the following rules
There will be no federal underpayment penalties if withholding and
1) timely estimated tax payments equal or exceed 90% of your 2022 tax
or
2) timely estimated tax payments equal or exceed 100% of your 2021 tax (110% if your 2021 adjusted gross income was more than $150K)
or
3) the balance due after subtracting taxes withheld from 90% of your 2022 tax is less than $1,000
or
4) your total taxes are less than $1,000
state laws differ
an oversimplified example: say you need to pay in $2000 for 2022 ($500 per tax quarter) and have $2000 withheld from an IRA distribution on say 12/15/2022.
using the normal method $500 would be deemed withheld each quarter so there is would be no underpayment penalty
now let's say you only have $1600 withheld on that date and pay $400 online the same day
now using the normal method only $400 is deemed paid each quarter so for the first 3 quarters you're underpaid $100 and are subject to the underpayment penalty. for the 4th quarter, you have $400 withheld and a $400 estimated tax payment which eliminates any penalty for the 4th quarter
there is no benefit in using the optional withholding method because you would be underpaid $500 for the first 3 quarters which would result in a higher penalty.
