Turning 65 in Colorado

There are two clocks running as you approach 65, and only one of them is the famous one. Missing the second is the more expensive mistake.

Turning 65 comes with a lot of mail. Most of it is trying to sell you something, and almost none of it explains the sequence. Here is the sequence.

Your Initial Enrollment Period

You get a seven-month window: the three months before your 65th birthday month, your birthday month itself, and the three months after. Enrolling in the three months before means coverage starts on the first day of your birthday month. Enrolling later delays your start date.

If you are already drawing Social Security, you are enrolled in Parts A and B automatically and your card arrives without you doing anything. If you are not, nothing happens until you act.

The window most people don't know about

Separately from the above, you get a six-month Medigap open enrollment period that starts the month you are both 65 and enrolled in Part B. During it, you can buy any Medicare Supplement policy sold in Colorado with no medical underwriting — no health questions, no denial for pre-existing conditions.

This window never comes back. Once it closes, buying a Medigap policy generally means answering health questions and being able to be turned down. People who take a Medicare Advantage plan at 65 and try to move to Medigap at 72 often discover that their health no longer permits it. More on what determines your Medigap premium →

If you are still working

If you or your spouse have active employer coverage from an employer with 20 or more employees, you can often delay Part B without penalty and pick it up later through a Special Enrollment Period. Under 20 employees, Medicare usually becomes primary and delaying can leave you badly exposed.

Two traps worth naming. First, COBRA and retiree coverage do not count as active employer coverage for delaying Part B — this catches people every year. Second, if you contribute to a health savings account, you must stop contributing before Medicare starts, and Part A can be backdated up to six months, which can create a tax problem retroactively.

The order we'd suggest

Three months out. Decide whether you are enrolling now or delaying because of employer coverage. If delaying, get the reason confirmed in writing.
Enroll in Parts A and B through Social Security, unless you are already receiving benefits and it happens automatically.
Choose your path: Medicare Advantage, or Medigap plus a standalone Part D plan. This is the decision your six-month Medigap window is quietly attached to.
Do not skip drug coverage, even if you take nothing today. The Part D penalty is permanent. More on Part D →
Check your doctors against the network before you enroll, not after.

Common Questions

Questions we get

About three to four months before your 65th birthday. Enrolling in the three months before your birthday month means coverage begins the first day of that month, with no gap. Waiting until after your birthday pushes the start date back.

Not always. If you have active employer coverage through an employer with 20 or more employees, you can usually delay Part B without penalty and enroll later through a Special Enrollment Period. If the employer has fewer than 20 employees, Medicare typically becomes primary and delaying can leave you underinsured. It is worth confirming which applies to you before you decide.

It is a six-month window starting the month you are both 65 and enrolled in Part B, during which you can buy any Medicare Supplement policy with no health questions. It does not come back. After it closes, Medigap carriers can generally use medical underwriting, which is why people who choose Medicare Advantage at 65 sometimes find they cannot move to Medigap later.

No, and this is one of the most costly misunderstandings we see. COBRA and retiree coverage are not treated as active employer coverage for the purpose of delaying Part B. Relying on either can produce a permanent late enrollment penalty and a coverage gap.

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Written and reviewed by Darin Weidauer — licensed Colorado insurance agent (NPN 18580338), Gerontologist (USC Davis School of Gerontology), MBA, Registered Social Security Analyst, and U.S. Air Force veteran. Independent and appointed with 10 Colorado carriers.Last reviewed September 2, 2026. Plan availability, benefits and costs change every plan year — verify current details at Medicare.gov or 1-800-MEDICARE.