Individuals who have an adjusted gross plus tax-exempt interest income more exceeding $85,000 (filing as a single) or $170,000 (married and filing jointly) will be subjected to a Medicare high-income surcharge on Parts B and D.
In 2017 monthly premiums for Part B were between $187.50 and $428.60 while Part D drug coverage meant an extra $13.30 to $76.20 per month.
Surcharges are based on last year's filed tax return. For 2017 premiums, individuals used their 2015 tax returns. If an individual's income changes due to life-altering events, they may request the Social Security Administration to provide a SSA-44 Form that re-evaluates the individual's income. Documentation will be required - divorce decree, employer salary statement, etc.
Head to Social Security Administration's Medicare Premiums: Rules for Higher-Income Beneficiaries for more information.