Underpayment tax penalty

[bebop]

A client filed as married filing joint in 2023 and married filing separate, not living together the entire year, in 2024. Does she have to use the joint tax liability from 2023 to determine if she has to pay a tax penalty? The program is putting the entire tax liability on form 2210, however, based on the clients income alone, had she filed separate in '23, she would not owe a penalty.

[sjrcpa]

Look at the 2210 Instructions.

[bebop]

I read the 2210 instructions before I posted my question.  I read them again after your reply. I am not seeing anything in the instructions addressing how to handle prior year tax liability when a person filed a joint return in the previous year and separate return the current year. Maybe I'm just missing it.  If you could be more specific and tell me what section in the instructions to find this, I would appreciate it.

[BobKamman]

I had to do a word search for "separate" to find the single sentence on Page 4 of the 2210 instructions that halfway answers this question. 

"If you file a 2024 return as single, head of household, married filing separately, but you filed a joint return with a spouse for 2023, your 2023 tax is your share of the tax on the joint return."

But how do you figure that?  In a community-property state it's easy, just take half.  Maybe.  But is "your share of the tax" computed with credits that aren't allowed on separate returns?  

Fill out the 2210 showing previous year as zero, and wait to see if there are enough warm bodies left at IRS to question it.