2026 IRMAA is based on your 2024 MAGI (adjusted gross income plus tax-exempt interest), and it works as a cliff: crossing a threshold by even $1 applies the full surcharge for that tier. This tool doesn’t cover Married Filing Separately, which has a different, compressed bracket structure. If you’ve had a qualifying life-changing event (retirement, death of a spouse, a significant income drop), you can file Form SSA-44 to request a recalculation. Confirm exact figures on Medicare.gov or your SSA determination letter, and talk to a tax professional about reduction strategies.