dupe question - agree with other comment to direct pay at irs.gov if able, avoid sending checks to IRS and state; and for this scenario you will get penalty if you split this payment evenly between Q3 and Q4 that won't work, believe you will be underpaid in Q3 whether you used default quarterly or AI method on Form 2210 - see https://ttlc.intuit.com/community/taxes/discussion/do-i-have-to-pay-penalties-on-a-large-roth-conver...
