(Image credit: Getty Images) If you have Medicare Part B or Medicare Part D prescription drug coverage, your monthly costs could look drastically different than the standard rates. High-income retirees are subject to the Income-Related Monthly Adjustment Amount (IRMAA) — a progressive surcharge added directly to your Medicare premiums if your income crosses specific thresholds. Understanding how the projected 2027 IRMAA brackets are calculated and how the two-year tax lag impacts you is essential to preserving your retirement savings. Failing to plan for these thresholds can trigger an unexpected financial "cliff," where a single dollar of excess income can cost you thousands in annual surcharges. This year, forecasting the 2027 numbers was more difficult because the Bureau of Labor Statistics (BLS) did not publish official CPI-W data for October 2025, due to the federal government shutdown last year.…