The taxable capital gains reported on the joint 2024 tax return increased the 2024 MAGI used to determine the 2026 IRMAA, so the IRMAA charge seems plausible. A $240.40 combined IRMAA for 2026 is the result of the 2024 MAGI being between $274,000 and $342,000.
2027 IRMAA will be based on 2025 MAGI. (2025 is 2 years prior to 2027.)
MAGI for this purpose is AGI (Form 1040 line 11) plus tax-exempt interest (line 2a).
Sammy should also have received a letter from Social Security. (If Sammy has elected not to receive this annual notification by mail, Sammy needs to log in to Sammy's Social Security account to obtain this).
