Short answer: An MPRA is an employer arrangement, generally for small employers with fewer than 20 employees, that reimburses Medicare-enrolled employees, tax-free, for their Medicare Part B, Part D, and Medigap premiums.
A Medicare Premium Reimbursement Arrangement (MPRA) lets a small employer help Medicare-enrolled employees pay their Medicare premiums on a tax-free basis. It reimburses Part B, Part D, and Medigap premiums; to meet the IRS conditions it must be limited to Part B or Part D premiums and excepted benefits such as Medigap.
MPRAs generally work only for employers with fewer than 20 employees, because that’s when Medicare pays primary and the Medicare Secondary Payer (MSP) rules don’t prohibit integrating with Medicare. At 20 or more employees, the group plan is primary and an employer may not steer or incentivize active employees onto Medicare. An MPRA must also meet the conditions in IRS Notice 2015-17 (for example, the employer must offer the employee a group health plan providing minimum value, and the employee must be actually enrolled in Medicare Parts A and B).