Millions of Americans with Medicare are about to get a small but welcome boost to their budgets. The federal government is sending one-time payments of $90 per person to help more than 20 million enrollees cover their Medicare Part B premiums. For many retirees, the money will show up with no paperwork or application needed.

The payment arrives at a time when health care costs keep climbing for older Americans. The standard Part B premium is $202.90 a month, a significant expense for anyone living on a fixed income. Part B covers outpatient care, doctor visits and certain medical services, which makes it one of the most widely used parts of Medicare. Even a one-time $90 can help offset that bill, whether it goes toward groceries, prescriptions or the next utility payment.

There is a catch, however. Not everyone enrolled in Medicare will receive the money. The eligibility rules leave out several large groups, including the millions of people who get their coverage through private Medicare Advantage plans. Others may be excluded because of how their premiums are paid or because of their income level. That means many seniors who assume they’ll get a check could be surprised to find nothing in their account.

The money comes from the Medicare Improvement Fund, which Congress created in 2008. The White House described this as the first time that fund has been used to send money directly to beneficiaries.

If you’re on Medicare, it’s worth taking a few minutes to understand whether you qualify, when the money should arrive, how it will be delivered and who to contact if something seems off.

Here we break down everything you need to know about the $90 payment, including the simple steps to check your eligibility and how to avoid the scams that often follow announcements like this one.