This variable is the number of months in the reference year that the beneficiary was determined to be eligible for a Part D premium low-income subsidy (LIS).
The Medicare Modernization Act of 2003 (MMA) mandated that CMS establish the LowIncome Subsidy (LIS) program for the Medicare Part D benefit, which provides subsidies that reduce or eliminate Part D premiums and deductibles and offers zero or reduced co-payments for low-income beneficiaries.
Beneficiaries who are eligible for the full LIS subsidy will pay zero premiums if they are enrolled in an at- or below-benchmark plan. If they enroll in above-benchmark plans, they are responsible for paying the amount of the premium above the benchmark. Because benchmarks are recalculated on an annual basis, some plans may be at or below the benchmark in one year but not in the following year.
Source: CMS Common Medicare Environment (CME) - derived