Medicare starts according to your eligibility, the part you enroll in and when you apply. Parts A and B can have different effective dates. Read the enrollment confirmation and your Medicare card before ending existing insurance.
At age 65
The usual Initial Enrollment Period lasts seven months: three months before your birthday month, that month and three months after. A birthday on the first day of a month shifts the schedule earlier. For example, a June 1 birthday generally uses February–August, and timely enrollment can begin May 1.
| Situation | Usual start date |
|---|---|
| Premium-free Part A at 65 | The birthday month; the preceding month for a first-day birthday. |
| Part B or purchased Part A: apply before the birthday month during the initial period | The birthday month, subject to the first-day-birthday adjustment. |
| Part B or purchased Part A: apply in the birthday month or one of the following three months | The following month. |
| General Enrollment Period, January 1–March 31 | The month after enrollment; a penalty may apply. |
Coverage begins on the first of a month. Do not rely on older articles saying every late initial-period application has a two- or three-month delay or that general enrollment always starts in July.
Delayed Part A and work-related enrollment
Premium-free Part A obtained after age 65 can be retroactive up to six months, but not earlier than initial eligibility. This can affect HSA contributions. It does not mean Part B or a private plan automatically receives the same retroactive start date.
A qualifying current-employment Special Enrollment Period generally lasts until eight months after employment or qualifying group coverage ends, whichever is earlier. Part B usually begins the following month. When applying while still working or within the first full month after employer coverage ends, you may be able to request a start delayed by up to three months. Confirm the requested date with Social Security.
Other special periods, disability and End-Stage Renal Disease have different rules. COBRA and retiree coverage do not extend the current-employment Part B deadline.
Confirm every layer of coverage
- Check the A and B dates separately.
- Obtain the Medicare Advantage or Part D plan’s own enrollment confirmation.
- Coordinate any Medigap start with Original Medicare and the end of other coverage.
- Tell the employer administrator about the confirmed transition dates.
- Ask Social Security promptly if an official date appears wrong.
A submitted application or premium payment alone is not confirmation that coverage is active.
Related coverage questions
- How to Enroll in Medicare: Steps, Timing and Where to Get Help
- Who Is Eligible for Medicare? Age, Disability and Enrollment
- How to Verify Your Medicare Coverage and Plan Enrollment