When one starts Medicare, Part B and Part D premiums are estimated using the income tax filing for 1 or 2 prior years. The premium is adjusted up or down when taxes are filed each year. You may initially be billed at the base rate and then receive a secondary notice on what additional cost will be added based on income. The following charts list the adjustments.
Below the charts, is the official booklet on Medicare premium adjustments and the SSA-44 form you will need to submit an appeal.