Medicare is not a need-based program like Medicaid, but instead, it is based on the accumulation of Social Security work credits. To qualify, a taxpayer needs 40 work credits, and as of 2015, one credit is earned for each quarter in which earnings topped $1,220.
Originally, the Social Security system used QCs, or quarters of coverage. A taxpayer earned one QC for any quarter in which he earned more than $50, so a taxpayer could earn Medicare coverage by making $2,000 over 10 years of work. The system changed in 1978 to work credits, and the amount to qualify for each credit is determined by comparing the 1978 benchmark of $250 per quarter to the current wage index.