Initial Enrollment Period (IEP) — your one shot at the best rights
Your IEP is the 7-month window centered on your 65th birthday: the three months before your birthday month, your birthday month itself, and the three months after.
If you're already receiving Social Security or Railroad Retirement Board benefits when you turn 65, you'll be automatically enrolled in Part A and Part B effective the first day of your birthday month. If you're not yet collecting Social Security, you need to actively enroll through SSA — either online at ssa.gov/medicare, by calling 1-800-772-1213, or in person at a Social Security office.
Two things to know about timing:
- If you enroll in the three months before your birthday month, your Medicare coverage starts the first day of your birthday month.
- If you enroll during or after your birthday month, coverage starts the first day of the following month.
The IEP is also when your Medigap Open Enrollment Period starts — a separate 6-month window beginning the month you're both 65 and enrolled in Part B. During this 6-month window, no Medigap insurer in Ohio can deny you coverage or charge you more based on your health. This is the only time most Ohioans have guaranteed-issue Medigap rights. Miss it, and outside of a few narrow Guaranteed Issue triggers, insurers can underwrite you.
If you're working past 65 with employer coverage
You can delay enrolling in Part B without penalty — but only if your employer plan qualifies. See our Working Past 65 guide for the rules. Note: HSA contributions must stop the month you enroll in any part of Medicare, including premium-free Part A.
General Enrollment Period (GEP) — January 1 to March 31
The GEP is the fallback for people who missed their IEP and aren't eligible for an SEP. Sign up between January 1 and March 31, and your coverage begins the first of the month after you enroll.
The bad news: if you sign up during the GEP, you may owe a late enrollment penalty — 10% added to your Part B premium for every full 12-month period you delayed. This penalty stays with you for the rest of your life on Medicare.
Annual Enrollment Period (AEP) — October 15 to December 7
This is the big one. Every fall, anyone with Medicare can:
- Join, switch, or drop a Medicare Advantage plan
- Join, switch, or drop a Part D prescription drug plan
- Switch from Original Medicare to Medicare Advantage, or vice versa
Changes you make during AEP take effect January 1. Medicare carriers send out their Annual Notice of Change (ANOC) letters by September 30 every year — these document what's changing on your current plan for the next calendar year. Read them. Premium changes, formulary changes, provider network changes, and benefit changes are all in there.
Medicare Advantage Open Enrollment (OEP) — January 1 to March 31
The OEP is a do-over period for people who are already enrolled in Medicare Advantage. If you started the year on an MA plan and regret it, between January 1 and March 31 you can make one change:
- Switch to a different Medicare Advantage plan
- Drop MA and return to Original Medicare (and pick up a standalone Part D plan)
Critical limitation: returning to Original Medicare during OEP does not automatically give you guaranteed-issue Medigap rights. In most cases you'll have to medical-underwrite. Plan G is hard to get back if your health has changed.
Special Enrollment Periods (SEPs) — for life events
SEPs are triggered by specific events. The most common ones in Ohio:
| Event | SEP length |
|---|---|
| Lost employer or union coverage | 8 months for Part B; 2 months for Part D |
| Moved to a new service area | 2 months from the move |
| Qualified for or lost Extra Help / Medicaid | Quarterly for the first 3 quarters of the year |
| Plan's contract with CMS ended or violated | 3 months |
| 5-star plan SEP (once per year) | Dec 8 – Nov 30 |
| Returned to U.S. after living abroad | 2 months |
| Released from incarceration | 2 months |
Late enrollment penalties
Three different penalties can attach if you miss enrollment windows:
Part B penalty: 10% added to your premium for every full 12-month period you could have had Part B but didn't. Permanent. If you delayed 4 years, you pay 40% more for life.
Part D penalty: 1% of the national base premium ($38.99 in 2026 = about $0.39) per month you went without creditable drug coverage. Also permanent.
Part A premium penalty: If you have to pay for Part A (because you didn't earn enough quarters), late enrollment adds 10% to that premium for twice the number of years you delayed.
The good news: most of these penalties are avoidable if you understand what counts as creditable coverage and you don't have an enrollment gap. If you're working past 65 with employer drug coverage, that's almost certainly creditable — your HR department can confirm and give you the annual notice that proves it.