IRMAA is an extra Medicare Part B and D premium based on income from two years prior, triggered when 2024 MAGI exceeds about $106,000 for singles or $212,000 for joint filers. Surcharges increase through five brackets, with Part B ranging from $81.20 to $487 and Part D from $14.50 to $91 monthly. IRMAA applies fully once a threshold is exceeded. Planning strategies include managing income, using charitable distributions, timing asset sales, and appealing due to life events.