When is the Medicare Initial Enrollment Period?

A seven-month window: the three months before the month you turn 65, your birthday month, and the three months after. Enrolling in the first three months generally gives the earliest coverage start date.

What happens if I miss my Medicare enrollment deadline?

If no Special Enrollment Period applies, you would generally wait for the General Enrollment Period from 1 January to 31 March, with coverage beginning the first of the month after you sign up, and a late enrollment penalty may be added to your premium — for Part B, typically for as long as you have it.

Can I delay Medicare Part B if I am still working?

Sometimes — it depends on the size of the employer and whether the coverage comes through current employment. Because getting it wrong creates a permanent penalty, confirm your specific case with the employer's benefits administrator and with medicare.gov or a SHIP counsellor before deciding.

Does COBRA count as creditable coverage for Medicare?

COBRA generally does not count as coverage through current employment for Part B purposes, so it usually does not create the eight-month Special Enrollment Period that ending active employment does. Check your own situation before relying on it.

When is Medicare Open Enrollment?

15 October to 7 December each year, for changing your existing coverage, with changes effective 1 January. People already enrolled in a Medicare Advantage plan have an additional window from 1 January to 31 March.

Medicare Enrollment Deadlines Explained: IEP, GEP, SEP and Open Enrollment

The four windows

1. Initial Enrollment Period (IEP) — seven months around your 65th birthday

It opens three months before the month you turn 65, includes your birthday month, and closes three months after. Signing up in the first three months generally means coverage starts the month you turn 65; signing up later in the window generally pushes the start date back.

2. General Enrollment Period (GEP) — 1 January to 31 March

The catch-up window if you missed your IEP and no special circumstances apply. Coverage now begins the first of the month after you sign up. A late-enrollment penalty may apply.

3. Special Enrollment Period (SEP) — after employer coverage ends

If you were covered by a group health plan through your own or a spouse's current employment, you generally get an eight-month window beginning when the employment or the coverage ends, whichever comes first, to enroll in Part B without penalty. This is the window most often missed by people who kept working past 65.

4. Open Enrollment — 15 October to 7 December

The annual window for changing what you already have: switching between Original Medicare and Medicare Advantage, or changing drug plans. Changes take effect 1 January. There is also a Medicare Advantage open enrollment period from 1 January to 31 March for people already in an Advantage plan.

The penalties, and why they matter

Two of them are permanent, which is what makes the dates worth attention.

Part B late enrollment penalty. Generally 10% added to your premium for each full 12-month period you could have had Part B and did not — and it usually lasts for as long as you have Part B.
Part D late enrollment penalty. Generally a small percentage of a national base premium for each month you went without creditable prescription drug coverage, added to your premium for as long as you have Part D.

The word doing the work is creditable. Coverage counts as creditable when it is expected to pay, on average, at least as much as standard Medicare drug coverage. Your plan has to tell you in writing each year whether yours is — keep that letter, because it is the evidence that prevents a penalty.

The three situations people get wrong

Still working at 65

Whether you can safely delay Part B depends on the size of the employer and whether the coverage is through current employment. The threshold is not the same for everyone, and getting it wrong is what produces the permanent Part B penalty. Ask the employer's benefits administrator, in writing, whether their plan is primary or secondary to Medicare in your case.

COBRA and retiree coverage

These generally do not count as coverage through current employment for Part B purposes, so they typically do not give you the eight-month Special Enrollment Period. This surprises a lot of people at exactly the wrong moment.

Health Savings Accounts

Once Medicare starts, you can no longer contribute to an HSA — and Part A enrollment can be backdated, which can create an overlap. If you are contributing to an HSA and approaching 65, this is a specific question to raise before you file anything.

What to do, in order

Write down your IEP dates — count three months back from your birthday month and three forward.
Establish what coverage you have now and whether it is through current employment. Get the answer from the benefits administrator, not from memory.
Find the creditable-coverage letter for your current drug coverage and keep it.
Call your SHIP. Free, unbiased, one-to-one, and not selling anything — it is the single best use of an hour in this whole process.
Diarise 15 October every year, because plan formularies and costs change annually even when nothing about you does.

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Common questions

When is the Medicare Initial Enrollment Period?: A seven-month window: the three months before the month you turn 65, your birthday month, and the three months after. Enrolling in the first three months generally gives the earliest coverage start date.
What happens if I miss my Medicare enrollment deadline?: If no Special Enrollment Period applies, you would generally wait for the General Enrollment Period from 1 January to 31 March, with coverage beginning the first of the month after you sign up, and a late enrollment penalty may be added to your premium — for Part B, typically for as long as you have it.
Can I delay Medicare Part B if I am still working?: Sometimes — it depends on the size of the employer and whether the coverage comes through current employment. Because getting it wrong creates a permanent penalty, confirm your specific case with the employer's benefits administrator and with medicare.gov or a SHIP counsellor before deciding.
Does COBRA count as creditable coverage for Medicare?: COBRA generally does not count as coverage through current employment for Part B purposes, so it usually does not create the eight-month Special Enrollment Period that ending active employment does. Check your own situation before relying on it.
When is Medicare Open Enrollment?: 15 October to 7 December each year, for changing your existing coverage, with changes effective 1 January. People already enrolled in a Medicare Advantage plan have an additional window from 1 January to 31 March.

General information — this is not medical advice, not insurance advice, and not affiliated with Medicare or any government agency. Rules and dates change. Confirm everything at medicare.gov or with your State Health Insurance Assistance Program (SHIP), which gives free, unbiased one-to-one counselling. This page does not tell you which plan to pick.