Monte Carlo runs simulations sampling annual returns from a normal distribution. Shows total portfolio value (IRA + Roth) percentile fan at each age.

IRMAA (Income-Related Monthly Adjustment Amount) increases Medicare Part B and Part D premiums based on MAGI from 2 years prior (SSA look-back). Roth conversions are fully included in MAGI and can push you into higher IRMAA tiers the year after next — e.g. heavy conversions at 63 affect Medicare costs at 65. MFS filers who lived with their spouse jump directly from the standard tier to the maximum tier above $106K. Thresholds are 2025 CMS values scaled for inflation annually. The "MAGI Used" column shows the look-back income SSA actually uses to set each year's tier.