How to allocate quarterly estimated taxes when some will be pd w RMD

[Arches National Park]

Paying 2024 estimated taxes w a combo of RMD & quarterly payments. Converted TIRA $ to Roth in 2023, so have higher than usual income. Will need to pay 110% of 2023 tax due (plus $1) for safe harbor. Plan to take RMD in late Nov and send the entire amount (less a few QCDs) to IRS. Using a sample number to make the math easy, let’s say we owe $50k for safe harbor and the $ withheld for taxes from the RMD will be $10k. 

Do we subtract the $10k RMD payment from the $50k due since it counts as spread the whole year and divide the remaining $40k by 4 and make 4 estimated payments of $10k each? A friend says we should divide the $40k by 3 and send $13333 for April, June, September, have the $10k withheld from the RMD in Nov as planned, and don’t send the Jan '25 payment. The #s computed by TT are way off bc the numbers are so different from prior year. What is the correct way to do this? Thanks for any help!

[ThomasM125]

The simple thing to do would be to divide the $50,000 tax by four and pay in $12,500 for three quarters and $2,500 for the fourth quarter when you will have $10,000 additional tax paid in from the RMD withholding. If you are usure of the tax due for 2024, you could use the tax from 2023 multiplied by 110% and then divide by four to determine the quarterly payments.

However, the additional tax due on the RMD isn't due until January 15 of 2025, so you could pay in less for the first three quarters and make up the difference in the fourth quarter. If you do that, you may have to use the annualized income method to determine any penalty for late payment of tax, by filing form 2210. That is a complication you may not want to bother with when you prepare your tax return.