Here's how to tell whether the surcharge applies in your retiree plan, Medicare officials say:

• If your former employer's retiree health care plan receives a retiree drug subsidy from the government, you are not liable for the Part D surcharge.

• If your former employer's retiree health care plan contracts with Medicare to provide Part D coverage — either through a Part D drug plan or through a health care plan that includes Part D drug coverage — you are liable for the Part D surcharge if your income is above the specified level.

• If your retiree plan pays your Part D premiums, the employer may choose to pay the surcharge also, when applicable, but is not obliged to. You should be aware that even if your former employer springs for the surcharge, you are still legally responsible for ensuring that it is paid each month.

Medicare officials say they've sent a memo to Part D plans so that "they could help provide information to employers to relay to their retirees about the Part D surcharge." So eventually, if your retiree drug coverage actually comes under Part D, you may receive details about the surcharge from your retiree plan.

In the meantime, if you receive a letter from Social Security saying that you owe the higher-income surcharge, call your retiree plan to ask whether it receives a drug subsidy from the government or contracts with Medicare to provide coverage under Part D — and, if the latter, whether it will pay the surcharge for you. Then you'll know whether the assessment is correct.

Finally, be aware that liability for the higher-income surcharge for both Part B and Part D is based on your latest tax return, which reflects income you received the previous year. If your income this year is substantially less than you were receiving two years ago because of certain "life-changing events" — which include retirement — you can request a reassessment. For details, see the Social Security document previously cited.

Patricia Barry is a senior editor for AARP Integrated Media.

Updated December 14, 2012

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