You can sign up for Medicare Part D, which helps cover prescription drug costs, along with other components of Medicare starting three months before your 65th birthday.

It’s important to do this on time because there’s a permanent premium surcharge for enrolling more than three months after your 65th birthday if you don’t have equivalent drug coverage from another source, such as a retiree plan.

If you choose Original Medicare:

If you want this coverage (Part D), you must choose and join a Medicare Prescription Drug Plan.

These plans are run by private companies approved by Medicare.

If you choose a Medicare Advantage Plan:

If you want prescription drug coverage, and it’s offered by your plan, in most cases you must get it through your plan.

In some types of plans that don’t offer drug coverage, you can join a Medicare Prescription Drug Plan.

If you are already enrolled in a Part D “standalone” plan or a Medicare Advantage plan that incorporates drug coverage, you can switch plans during the open-enrollment period, which runs from Oct. 15 to Dec. 7 every year.

Choosing a good plan

It pays to review your Part D coverage every year, especially if you have started taking new drugs.

Start at Medicare.gov. You can find the basics about the benefit and Part D plans at Medicare’s website. There’s a link to the Medicare Part D Plan Finder, which allows you to compare offerings and coverage options in your area and includes a helpful formulary finder that allows you to compare plans based on their coverage of your personalized list of drugs. It will even show you your monthly out-of-pocket drug cost for the year.