Recently we wrote about open enrollment season, that annual autumn rite where employees with health care coverage at work get to choose their medical benefits for the coming year.

This week, it's about the other side of open enrollment: Medicare coverage, which is primarily for retirees ages 65 and older. If that's you, your open enrollment season started Oct. 15 and runs through Dec. 7.

As everyone knows, health care choices can be confusing. To get some clarity, we talked with Nancy Metcalf, a health care specialist with Consumer Reports based in Yonkers, N.Y., who's been writing, blogging and answering online questions about Medicare and health care coverage for the past five years.

You've cited studies that say one in four Americans don't realize they can switch their Medicare plan every year. Why is that?

People are creatures of habit. They don't check every year and realize they can switch. But prices can creep up … prescription drug costs, co-pays, co-insurance. Or your doctor or hospital can leave your covered group.

Chances are your plan won't be that different (every year) but it can still pay to check.

What are the best ways to figure out Medicare choices?

It can be really confusing. I've been doing this intensively for five years and every day I get questions I don't have answers to. It's like learning a foreign language.

That's why consumers should use state health insurance assistance programs. Every state has one. You can call an 800 number and get free Medicare counseling. (See accompanying box for details.)

You can also go to Medicare.gov, the federal consumer website, which has free online comparisons and ratings of various Medicare plans. Based on your ZIP code, you can compare the choices available to you.

Where do Medigap policies come in?

Medicare does not cover everything. You still have to pay out of pocket. This year, the Part A deductible is $1,156 if you go in the hospital. For Part B, there's a $140 deductible, plus 20 percent of everything over that. If you have outpatient therapy for cancer, it could be $10,000 a month, so your share would be $2,000. It can really add up to big money.

One way to avoid that is to get a Medigap plan, which pays what Medicare doesn't. It keeps you from that financial vulnerability. They're sold by private insurers all over the country and come in different "flavors," depending on what you want.

If you want minimum billing hassles and automatic payments to your insurer, go on original Medicare with a Medigap plan. After Medicare pays its portion, they send the difference on to Medigap that covers the remainder.

So who should choose a Medicare Advantage plan?

You can see why seniors are completely baffled.

The advantage of Medicare Advantage plans is a lower premium up front. Many have no premiums whatsoever or only $25 a month. But they come with co-pays, deductibles, co-insurance. The annual out-of-pocket limit can range from $3,000 to more than $6,000. Once the deductibles and copays out of your own pocket reach this limit, the plans cover 100 percent of your costs through the end of the calendar year. Premiums do not count towards the out-of-pocket limit.

Unlike original Medicare, they are almost all HMOs, so each plan has a provider network of doctors. That means if your doctor isn't in your network, your treatment will not be covered.

How do people choose between Medicare (with a Medigap supplement) or a Medicare Advantage plan?

There's no right answer; especially in California, which has one of the best Medicare Advantage plans in the country: Kaiser, which dominates the best 5-star plans.

You can compare all the plans and their ratings, based on patient satisfaction, preventive care, chronic illness, etc., using the "Medicare Plan Finder" at Medicare.gov.

What should consumers know about buying Part D prescription drug coverage?

Part D started in 2006 and is only purchased through private insurance companies. The average premium costs about $30 a month. Many, many companies offer them.

But your out-of-pocket costs can change dramatically. Take a heartburn drug like Nexium. It might cost $250 in one plan and $20 in another, depending on what kind of arrangement the (health plan) provider has with various drug manufacturers.

As an example, I took a reader's ZIP code and typed in two typical pharmacies and a typical list of three drugs that a retiree might take: 10 mg of generic Lipitor, 75 mg of generic Plavix, and 40 mg of Nexium, a brand-name drug.

About 30 plans came up and the price difference was really striking. The cheapest plan cost $744 a year and the most expensive was $3,915.

When choosing a Part D plan, you also need to look at what other features you might want. If you're a senior who travels a lot, some Part D plans offer a national pharmacy network.

What if you figure you're healthy and don't want to pay for Part D?

There's a penalty for both Part B and Part D, if you don't sign up when you first become eligible (age 65).

It's a mistake a lot of people make: "I'm healthy, I do yoga, I eat right, I don't take any medications."

Fine, except you get something serious like a cancer or an autoimmune disease and need a drug that's $2,000 a month. You'd have to wait until the next open enrollment period to sign up.

If you delay, you'll be assessed penalties on your monthly premium for every month that you could have been signed up.

What are the biggest mistakes people make in selecting their Medicare plans?

This time of year, people are getting an inundation of promotional mail from companies saying "Buy My Plan." It's only $30 a month; it's so easy to sign up.

But people often make two mistakes: They might buy a Medicare Advantage plan and think it's a Medigap supplemental plan.

Or if they're not comparing, they'll sign up for a not-very-good plan that is too expensive, has a lower quality rating or their doctor is not on it.

To see more of Metcalf's advice: Go to www.ConsumerReports.org and search for "Managing Medicare."

MEDICARE AT A GLANCE

Medicare – The original, federal health insurance plan for those 65 and older (or younger individuals with disabilities). It provides coverage for hospital care (Part A) and medical services (Part B). There is a monthly premium, plus some deductibles and co-insurance.

Medigap – A supplemental plan for costs not covered by original Medicare, such as co-payments and deductibles. It does not cover prescription drug costs. Premiums and services covered can vary widely. (Note: A Medigap plan is only for regular Medicare subscribers; it can't be purchased if you have a Medicare Advantage plan.)

Medicare Advantage – Referred to as Part C, these plans are offered through Medicare-approved private insurers in every state. In addition to covering Part A and Part B, most MA plans cover prescription drugs, as well as dental, vision and hearing aids. They typically offer lower premiums than regular Medicare, but you must use specific doctors

Prescription Drug – Known as Part D, this insurance covers prescription drug costs for both original Medicare or MA plans that don't cover drugs. It carries a monthly premium and is run by Medicare-approved private insurers.

Helpful resources

HICAP – Sponsored by the California Department of Aging, the Health Insurance Counseling & Advocacy Program offers free, one-on-one counseling for individuals with Medicare questions. To schedule an appointment at one of its statewide offices, call (800) 434-0222 or visit: www.cahealthadvocates.org. (Note: During current Oct. 15-Dec. 7 open enrollment season, phone messages can take up to three days to return)

Medicare.gov – Official U.S. government Medicare website, offering plan comparisons, Q&As on prescription drug coverage, etc. Or call (800) MEDICARE (633-4227); your Medicare number is needed to access phone services.

ConsumerReports.org – Search under "Managing Medicare" for tools, tips, Q&As on all aspects of Medicare

Editor's note: An earlier version of this story included misinformation about Medicare Advantage plans. It has been updated to correctly state: The annual out-of-pocket limit on Medicare Advantage plans can range from $3,000 to more than $6,000. Once the deductibles and copays out of your own pocket reach this limit, the plans cover 100 percent of your costs through the end of the calendar year. Premiums do not count towards the out-of-pocket limit.

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