In order to be eligible for Medicaid (as a full dual-eligible beneficiary, or for partial assistance with things like Medicare premiums and out-of-pocket costs) or Extra Help financial assistance, a Medicare beneficiary must have income that doesn’t exceed certain percentages of the federal poverty level (eligibility varies depending on the program, with more assistance available to people with lower incomes; asset tests are also common, meaning that the beneficiary must have limits assets in addition to a fairly low income in order to qualify for assistance through the Medicaid program).
The FPL, which changes annually and is published each year by HHS, is $12,140 for a single person in 2018.