Turning 65 triggers a single enrollment window that never repeats: the Initial Enrollment Period, or IEP. Unlike each fall's AEP or each spring's OEP, the IEP is personal — it is built around your own birthday — and the decisions you make inside that window can affect your coverage and premiums for years. This guide focuses specifically on the IEP: how the window works, what you can enroll in, what happens if you are late, and how it differs from the other enrollment periods.
What exactly is the Initial Enrollment Period
Your IEP is a seven-month window built around the month you turn 65: it starts three months before that month, includes your full birthday month, and continues three more months after. The calculation is the same for everyone regardless of the exact day of the month you were born, and it is the first opportunity most people get to enroll in Medicare based on age, rather than disability.
If you already receive Social Security or Railroad Retirement benefits before turning 65, you will likely be automatically enrolled in Part A and Part B, and your Medicare card will arrive in the mail a few months before your birthday. If you are not yet receiving those benefits, enrollment is your responsibility, and it does not happen automatically.
How your enrollment timing affects when coverage starts
Timing within your seven-month window matters. If you enroll during any of the three months before your birthday month, your coverage generally starts the first day of your birthday month. If you enroll during your birthday month or in the three months after, your start date is delayed, typically to the month following your enrollment, which can leave you several weeks or months without active coverage while you wait.
That is why I recommend starting to compare plans at least two or three months before your birthday month, even if you do not plan to enroll right away. Having time to review options without rushing avoids last-minute decisions near the edge of the window.
Which parts of Medicare you can enroll in during your IEP
During your IEP you can enroll in Part A (hospital insurance, generally premium-free if you or your spouse paid enough Medicare taxes during your working years) and Part B (medical insurance, which carries a monthly premium). Once your Part A and Part B are active, that same window also lets you choose between staying on Original Medicare — adding, if you want, a standalone Part D plan and possibly a Medigap plan — or enrolling in a Medicare Advantage (Part C) plan that bundles hospital, medical, and, in most cases, drug coverage into one plan.
Our Part A guide, Part B guide, and Medicare Advantage vs. Original Medicare guide explain each path in more detail before you decide.
If you are still working past 65
Not everyone should enroll in Part B exactly at 65. If you or your spouse are still working and have creditable coverage from an employer with 20 or more employees, you can delay Part B without penalty until that coverage ends, at which point an eight-month Special Enrollment Period opens. Many people in this situation still take premium-free Part A at 65, but it is worth reviewing your specific case — including whether you have a health savings account (HSA) — before deciding. Our guide on turning 65 while still working covers these scenarios in more detail.
What happens if you let your IEP pass without enrolling
If you do not have creditable employer coverage and let your IEP pass without enrolling in Part B, you will typically have to wait for the General Enrollment Period, January 1 through March 31, and your coverage will not start right away. On top of that, Medicare can add roughly 10 percent to your monthly Part B premium for each full 12-month period you were eligible but did not enroll — a penalty that generally applies for as long as you have Part B, not just for one year.
Part D carries its own penalty if you go 63 or more days in a row without creditable drug coverage after your IEP ends. Both penalties are avoidable by reviewing your exact eligibility date ahead of time, and they are one of the main reasons this window should not be allowed to pass by accident.
Availability, cost, benefits, and eligibility vary by person, product, contract, and insurance company, as well as by your service area. Guarantees are subject to the claims-paying ability of the issuing insurance company. Karla Arámburo is not affiliated with or endorsed by Medicare or the federal government.
How the IEP differs from AEP, OEP, and SEP
The IEP is unique because it happens only once in your life, around age 65, and it is the doorway into Medicare itself. The other periods — each fall's AEP, each spring's OEP for people who already have an Advantage plan, and the SEPs that open for specific events like a move — exist to adjust coverage you already have, not to enroll for the first time. If you have already been through your IEP and want to understand when you can make changes going forward, our AEP vs. OEP vs. SEP guide compares those three later windows in detail.
How I can help during your Initial Enrollment Period
Karla Arámburo is an independent, bilingual, licensed insurance agent serving Southern California, and reviewing your IEP with her costs nothing and comes with no pressure to enroll. Together we compare the Medicare Advantage, Part D, and Medigap plans available for your ZIP code, confirm whether your current doctors and medications are covered, and work out the exact date you need to act so your coverage starts without a gap. I also offer life insurance options that accept an ITIN for families without a Social Security number. You can call or text (619) 321-8733 to schedule a conversation in English or Spanish before your enrollment window gets close.
Frequently asked questions
Exactly when does my Initial Enrollment Period start and end?
It starts three months before the first day of the month you turn 65, includes your entire birthday month, and ends three months after. That is seven months total, and the window is the same regardless of which day of the month you were born.
If I'm still working and have employer coverage, do I have to enroll in Part B at 65?
Not always. If your (or your spouse's) employer coverage is from an employer with 20 or more employees and counts as creditable, you can delay Part B without penalty until that coverage ends, at which point you get an eight-month Special Enrollment Period. Many people still enroll in premium-free Part A at 65, but it is worth confirming your specific situation before deciding.
Can I enroll in a Medicare Advantage plan during my IEP?
Yes. Once your Part A and Part B are active, your IEP is also your first opportunity to enroll in a Medicare Advantage (Part C) plan or a standalone Part D plan, instead of staying on Original Medicare alone.
When does my coverage start if I enroll during my birthday month or later?
If you enroll during the three months before your birthday month, coverage usually starts the first day of that month. If you enroll during your birthday month or in the three months after, your start date is delayed — generally to the month after you sign up — so enrolling earlier avoids weeks or months without active coverage.
What happens if I let my IEP pass entirely without creditable coverage?
You will typically have to wait for the General Enrollment Period, January 1 through March 31, with coverage that does not start right away, and you are likely to face a permanent Part B penalty and, if applicable, a Part D penalty as well. That is why it is worth confirming your exact date ahead of time, even if you feel healthy.
Is the IEP the same as a Special Enrollment Period (SEP)?
No. The IEP is the one-time seven-month window everyone gets around age 65. A SEP is a separate, later window that opens only if you qualify due to a specific event, such as losing employer coverage or moving. Our AEP, OEP, and SEP guide explains those later windows in more detail.
Can I change my mind after enrolling during my IEP?
You have some flexibility within your own IEP to adjust your choice while the window remains open, and after that, each fall's AEP and, if you have an Advantage plan, the January–March OEP give you regular opportunities to make changes.