Dear Rusty: I am confused by an article in my local newspaper which said that “MAGI” (modified adjusted gross income), on which my Medicare Part B premium is based, is my Adjusted Gross Income, plus any non-taxable interest, plus 50% of the social security I received. The part that is confusing is the 50% part. When I look at my tax return my Adjusted Gross Income includes the taxable portion of my Social Security benefit which, in my case, is 85% of my total benefits. Why must 50% of benefits be added to my AGI if it is already included in my total AGI? Signed: Confused