Note: This article was originally published Nov. 4, 2025.
As a federal health insurance program, Medicare may be straightforward, but navigating its various components and supplemental options can be a challenge.
Generally, U.S. citizens and legal residents 65 and older are eligible for Medicare. People younger than 65 who receive Social Security Disability Insurance, or those with end-stage renal disease or ALS, also qualify.
Medicare is made up of “parts.” Original Medicare constitutes Parts A and B. Part D, which covers prescription drugs, is optional, as is Medicare Supplement Insurance, also called Medigap. Then there’s Medicare Advantage, often called Medicare Part C, a separate insurance plan that includes Parts A and B, usually Part D, as well as other benefits.
“When you transition to Medicare, I think it can be complicated because of the choices,” says Samuel Skootsky, MD, chief medical executive of the UCLA Health Medicare Advantage Plan and chief medical officer of the UCLA Health Faculty Practice and Medical Group.
Among the biggest misconceptions about Medicare is that it’s free, he says. It’s not. And Medicare alone doesn’t cover all health care expenses.
There’s no monthly premium for Medicare Part A, also known as hospital insurance, for people who’ve paid Medicare taxes in the United States for at least 10 years. People whose spouse paid such taxes also are eligible for Medicare.
But there’s a standard monthly premium for Part B — which covers doctor visits, emergency care and other medical services — that can cost a few hundred dollars, depending on one’s income in retirement. Original Medicare only covers about 80% of health care expenses, excluding prescription drugs. This is where Medicare Supplement Insurance or a Medicare Advantage plan can help.
Here’s what you need to know about Medicare: when to sign up, how to make sense of the various parts, and the ins and outs of supplemental insurance and Medicare Advantage.
When to sign up for Medicare
People are eligible to enroll in Medicare during a seven-month window called the “initial election period” around their 65th birthday — three months before, the month of, and three months after. However, those who have health insurance through their employer or their spouse’s employer (provided it’s a company with at least 20 workers) can continue with their existing coverage. After retirement, they have eight months to enroll in Medicare to avoid “late enrollment penalties” that continue in perpetuity.
People who are not employed or work for a company with fewer than 20 employees generally must enroll in Medicare during the seven-month window of eligibility to avoid these fees.
Understanding Original Medicare: Parts A and B
Original Medicare comprises Parts A and B. Part A is for hospitalization, hospice, skilled nursing facility care and home health care. Part B helps cover doctor visits, emergency care and routine outpatient hospital services, such as diagnostic tests and lab and radiology services. When someone enrolls in Medicare, they are enrolling in these two parts, which together cover about 80% of health care expenses, except for prescription drugs.
There is a monthly fee for Part B, which is typically deducted from one’s Social Security check. People who aren’t receiving Social Security are billed quarterly for their Part B premiums. The premium for Part B is based on standard adjusted gross income. The standard monthly premium in 2026 for an individual whose annual income in retirement is $109,000 or less was $202.90.
Because Original Medicare only covers about 80% of health care expenses, most people opt for Medicare Supplement Insurance (Medigap) or enroll in a Medicare Advantage plan to cover the other 20%, says Scott Salmon, an independent insurance agent who helps people figure out what Medicare plans best suit their needs.
In Los Angeles County, about 60% of Medicare beneficiaries use a Medicare Advantage plan, Dr. Skootsky says.
What is Medicare Advantage?
Medicare Advantage is a separate insurance plan that bundles Parts A and B, the prescription drug coverage of Part D, as well as other benefits, such as routine vision and dental care.
The real advantage of a Medicare Advantage plan is “financial and administrative simplicity,” says Dr. Skootsky, adding that many Medicare Advantage plans offered in Los Angeles County have no additional premiums beyond the standard Part B charges.
“There’s just kind of life simplification,” he says. “It’s more predictable costs. There’s an out-of-pocket maximum. But what do you give up for that? You give up a little bit of choice,” particularly with Health Maintenance Organization (HMO) plans.
With an HMO plan, you select a primary care physician and network of providers for all your health care services.
“So if you said, ‘If I had cancer, and wanted to go wherever I want to get my cancer treated,’ an HMO may not be the best for me,” Dr. Skootsky says.
A Preferred Provider Organization (PPO) plan allows for greater flexibility to doctors and specialists.
However, all Medicare Advantage plans have more restrictions than Original Medicare, which allows participants to go to any doctor or hospital in the U.S. that accepts Medicare.
Medicare Supplement Insurance
Another option is supplemental Medicare insurance, which preserves the flexibility of Original Medicare while covering the balance of health care costs.
Various insurance companies offer Medicare Supplement policies, with premiums typically determined by a person’s age and where they live, Salmon says. Parts A and B and Medicare Supplement Insurance still don’t cover prescription drugs outside of a medical setting. So, for example, anesthesia or chemotherapy drugs received while in the hospital are covered, but not the cholesterol medication or blood thinners you may take at home. Prescription coverage would be obtained through a separate Part D plan sold by private carriers.
Even with a Medicare Supplement coverage plan, Original Medicare doesn’t include vision or dental benefits, which are sold separately.
These plans can cost several thousand dollars a year, Dr. Skootsky says. Which approach is best for you depends on your income, location and health needs.
With so many options, many people turn to insurance agents to help them navigate their choices, he says, though this can also increase costs.
Enrollment periods
Just like with medical insurance provided by an employer, there are limited times during the year when individuals can change their coverage or choose a different Medicare plan. Initial enrollment in Medicare and any additional plans, however, is timed to one’s 65th birthday or retirement from employer-provided insurance after age 65.
The Medicare annual enrollment period is Oct. 15 to Dec. 7, when people can join, drop or switch plans. People with Medicare Advantage can make changes during the Medicare Advantage open enrollment period from Jan. 1 to March 31, either switching plans or returning to Original Medicare.
People enrolled in Medicare Advantage or a standalone Part D drug plan should have been mailed a booklet called the Annual Notice of Change by the end of September, Salmon says. This document outlines the changes being made to plans each year. So if the medication you need or the provider you love is no longer covered by your plan, you know to change things up during the open enrollment period.
Thankfully, you don’t have to navigate all this information alone. The California Department on Aging provides free and objective information about Medicare.
Related article
Need help enrolling in Medicare? Here's a guide to terms you'll encounter
When is Open Enrollment for health insurance 2027?
