Medicare surcharges are set by your tax return from two years earlier, so a one-time income spike can raise premiums later.
Most people picture Medicare premiums as a flat, predictable line in the retirement budget. For higher-income beneficiaries, though, the amount owed is tied to a tax return filed years earlier, and a single unusual year can quietly push the cost up long after the money was spent. The surcharge that does this is called the…