Open enrollment for Medicare is underway through Dec. 7, so if you’re in the program and want to switch plans, now’s the time to shop.

Each year, more and more people choose privately run Medicare Advantage plans that work like traditional health insurance, rather than original Medicare. Thirty-one percent of Medicare beneficiaries are on a Medicare Advantage plan as of 2016, according to the Kaiser Family Foundation.

If you’re happy with your Medicare, you don’t have to change anything, but knowing all your options can’t hurt. Here’s how to shop for a Medicare Advantage plan.

Go to the Medicare Plan Finder on Medicare.gov. This website will ask for your prescriptions, but Patricia Barry, AARP Media features editor and author of “Medicare for Dummies, 2nd Edition,” suggests you first do a search without inputting your drugs. (After answering the Plan Finder questions, choose not to enter your drugs now and continue on to the list of plans.)

“Entering the drugs first can distort the results,” Barry says. The website may identify the “best” plans as those “that provide a good deal on drugs, but charge more for doctors’ visits and hospital stays than other plans,” she explains.

Get cost information by clicking on each plan’s title, then on the “benefits” tab. Don’t look solely at premiums; look also at copays, coinsurance and the deductible. Often, a high deductible is the trade-off for a lower premium.

Pay special attention to how well each plan pays for services you use most — any plan that doesn’t cover your needs isn’t a good deal. If you need dental, hearing or vision benefits, look for plans with colored circles containing D, H or V.

Just like regular health insurance, Medicare Advantage plans are largely a mix of health maintenance organizations (HMOs) and preferred provider organizations (PPOs). Sixty-four percent of Medicare Advantage enrollees choose HMO plans, according to the Kaiser Family Foundation, but you may prefer a different structure.

HMOs usually require you to select a primary doctor who coordinates your care. They also usually require a referral from that doctor if you want to see specialists. Often, HMOs pay nothing when you don’t use their doctors, except in an emergency.

A PPO will allow you to see any doctor you want, but you’ll pay less if you choose an in-network doctor.

“HMOs generally cost less but offer fewer providers to choose from,” says Kip Piper, a Medicare consultant and speaker in Washington, D.C. “Conversely, PPOs offer more choice but at a higher cost.”

Most doctors take original Medicare, but some do not take certain private plans like Medicare Advantage. If you like your doctors now, make sure they’re part of your plan’s network.

The easiest way to find out is to call the doctor’s office. The staff can tell you whether the doctor participates in the insurance plan you’re considering.

By now, your plan options should be narrowed to just a few. Write down the plan names and click on “Enter Information” under the big blue buttons on the Plan Finder. Do the search again, this time entering your drug names.

The new results will include only plans that cover your prescriptions. If one or more of the plans you chose before are listed, these are your finalists.

Medicare shoppers have one advantage over the rest of us: The star rating system, which tells you the quality of each plan on a one- to five-star scale. The ratings, determined by the Centers for Medicare & Medicaid Services, are based on several measures, such as benefits, customer satisfaction and how well the plan manages chronic conditions, Barry says.

The ratings system is new and isn’t perfect, Piper says, because it favors plans with healthier members. “Plans that serve more complex, high-needs patients tend to receive lower star ratings even though their real performance is likely quite good,” he says.

Nonetheless, shoot for a star rating of 3.5 or better. After you’ve selected a plan, you’re done — your old insurer (or Medicare) will be notified automatically of the switch.

Lacie Glover is a staff writer at NerdWallet, a personal finance website. Email: lacie@nerdwallet.com. Twitter: @LacieWrites.

This article was written by NerdWallet and was originally published by USA Today.

The article How to Choose a Medicare Advantage Plan originally appeared on NerdWallet.