For Part B — doctor’s visits and outpatient care — premiums are based on income. The standard premium this year is $135.50 a month , but financial help is available for people with low incomes who don’t qualify for Medicaid, the government health program for the poor, which covers just about everything.

Richer Medicare beneficiaries — individuals with annual incomes over $500,000 — pay $460.50 a month . Premiums are typically deducted from people’s Social Security checks. Part B also has a deductible of $185 a year, and co-payments of 20 percent after you reach your deductible.

Many people buy supplemental “Medigap” insurance to cover Medicare’s out-of-pocket costs.

Unlike Affordable Care Act plans, Medicare has no cap on out-of-pocket spending, so the cost can climb quite high for sick people. An analysis by the nonpartisan Kaiser Family Foundation found that Medicare enrollees in fair or poor health spent an average of $6,128 in 2013, or 47 percent of average Social Security income.

Prescription drug costs can also be high in Medicare, and they represent one of the most complex, confusing parts of the program. Medicare Part D plans are run by private insurers, and the premiums cost $40 a month on average this year, according to Kaiser. There are also annual deductibles before coverage kicks in — they are capped at $415 this year — plus co-payments and coinsurance. But if your income is low enough, you may qualify for extra help paying for drugs, and in some cases, owe no premiums or out-of-pocket costs.

Then, there is the dreaded “doughnut hole” — a gap in which the Medicare drug plans don’t pay for patients’ medications after they have spent a certain amount — this year, $3,820. At that point, enrollees have to pay 25 percent of the cost of brand-name drugs, and 37 percent of the cost of generic drugs, until their total out-of-pocket spending has reached $5,100. Once they hit that, they qualify for “catastrophic coverage,” and only pay a small co-payment for covered drugs for the rest of the year.

Kaiser recently found that one million Medicare beneficiaries had out-of-pocket spending above the catastrophic threshold in 2017, averaging $3,214.

What is Medicare Advantage?

Medicare Advantage is an increasingly popular alternative to traditional Medicare. Advantage plans are offered by private insurers that have contracts with Medicare. These plans have all the same benefits as traditional Medicare, and often more, such as dental care or health club memberships. Co-pays and deductibles vary depending on the plan. Unlike traditional Medicare, all Medicare Advantage plans have limits — $6,700 this year in most cases — on out-of-pocket spending.