Deceased on 12/21/2024.

Deceased had a small amount of income (int and div < $500) from 12/21 to 12/31/2024 that was reported on her final 1040.

The trustee wants a calendar year tax return.

I could file a 2024 Form 1041.  I think I need to report a 2024 Form 1041. An option is not to file one, in which case the 2025 Form 1041 would have a start date of 1/1/2025. And a mismatch of start date and date of death would be noticed by the IRS. Then an IRS notice would be sent to my client.

The 10 days of income on the Final 1040 is immaterial.