If you're enrolled in a regular Part D drug plan or a Medicare Advantage health plan that includes drug coverage — in other words, a plan that you've chosen from Medicare's menu of plans, that you pay for yourself and that has nothing to do with retiree benefits — the issue is quite clear. If your income makes you liable for the surcharge, you pay the required amount on top of your plan's premium. In 2013, the surcharge ranges from $11.60 to $66.40 a month, depending on your adjusted income level.

But what if you get prescription drug coverage from a former employer, as you do? It's an issue that will come up time and again relating to the new Part D surcharge, because millions of Medicare beneficiaries receive prescription drug coverage through retiree plans.

According to Medicare officials, "a lot of people think they have [purely] retiree drug coverage, but the employer actually contracts with a Part D plan." That means people are not always aware that they are in a Medicare employer group plan where the Part D surcharge would apply.

Next: Does the surcharge apply in your retiree plan? »