The Internal Revenue Service supplies your tax filing status, your adjusted gross income, and your tax-exempt interest income to the Social Security Administration to determine if you have an income related monthly adjustment amount (IRMAA). The Social Security Administration will add your adjusted gross income together with your tax-exempt interest income to get an amount called the modified adjusted gross income (MAGI).
The income-related monthly adjustment amount is effective from January 1 through December 31 each calendar year. The Social Security Administration will refigure your Medicare Part B premium amount again next year when the Internal Revenue Service updates the information.