Medicare Enrollment Checklist (2026) | Education

This checklist walks you through the three Medicare enrollment windows and the decisions that matter inside each. It's organized as a decision tree: start at the top, answer the questions in order, and you'll land in exactly one of the three windows with a concrete enrollment date.

Most Medicare-related five-figure mistakes come from missing this checklist or running it too late. Run it at least 6 months before your 65th birthday — ideally 12 months before — so you have time to coordinate with employer benefits, HSA contributions, and any retiree health coverage decisions.

Step 1 — Find your Initial Enrollment Period (IEP)

The IEP is a seven-month window centered on the month you turn 65:

The 3 months before your birth month
Your birth month
The 3 months after your birth month

If you were born in	Your IEP runs from	To
January	October (prior year)	April
February	November (prior year)	May
March	December (prior year)	June
April	January	July
May	February	August
June	March	September
July	April	October
August	May	November
September	June	December
October	July	January (next year)
November	August	February (next year)
December	September	March (next year)

Action: Write your IEP start and end dates on a calendar reminder. The clock for the late-enrollment penalty starts the day after your IEP ends, so the IEP end date matters as much as the start.

Step 2 — Decide if you'll have a Special Enrollment Period (SEP)

The SEP is the only way to delay Medicare past age 65 without triggering a late-enrollment penalty. It opens only when qualifying employer health coverage ends.

Answer in order:

At age 65, will you (or your spouse) still be actively employed at a job that provides health insurance?
- No → No SEP available. You must enroll during the IEP to avoid the Part B late-enrollment penalty. Skip to Step 4.
- Yes → continue.
Is the employer-provided plan considered "creditable coverage" for Medicare purposes?

Almost all active employer group health plans qualify. Plans that do not qualify include: COBRA, retiree-only plans, ACA Marketplace plans (in most cases), TRICARE-for-Life-only coverage, and VA-only coverage. If the plan is not creditable, the SEP does not apply — see Step 3 for the alternative.

Verify with HR or your benefits administrator in writing. Get the answer on letterhead before you make a delay decision.
Does the employer have 20 or more employees?
- Yes → Medicare is the secondary payer; the employer plan pays first. You can typically delay Part B without penalty as long as the active coverage continues, and the SEP gives you 8 months after coverage ends to enroll.
- No (fewer than 20 employees) → Medicare is the primary payer at 65 even if you have employer coverage. You should enroll in Parts A and B during your IEP; the small-employer plan pays second. Skipping enrollment leaves you uninsured for primary medical care.

If you have qualifying creditable coverage at a 20+ employee employer, you have a valid path to delay Medicare past 65. Your SEP starts the month after either employment or the coverage ends, whichever comes first, and runs for 8 months. Skip to Step 5.

Step 3 — If the SEP doesn't apply, beware the General Enrollment Period (GEP)

The GEP runs January 1 through March 31 every year. Coverage begins the first of the month after you enroll (so a January enrollment means February 1 coverage, a March enrollment means April 1 coverage).

The GEP exists as a fallback. If you missed your IEP and don't qualify for an SEP, you'll wait for the GEP. But by the time you fall back to the GEP:

The Part B late-enrollment penalty has already been accruing since your IEP ended. It's permanent and applies for as long as you have Part B.
You may have gone without insurance for several months, depending on when in the year you fell out of coverage.

Avoid the GEP if at all possible. Use Step 2 to confirm whether you qualify for an SEP, and Step 4 if you don't.

Step 4 — IEP enrollment action plan

If you're enrolling during your IEP (not delaying via SEP), here's what to do and when:

Months before 65	What to do
6 months	Confirm with HR whether you have Medicare-coordinating retiree coverage. Decide on Medigap vs. Medicare Advantage. Stop HSA contributions if any.
4 months	Open a "my Social Security" account at ssa.gov/myaccount. Apply for Medicare via the SSA website (it's the front door for Parts A and B).
3 months	Finalize your Part D drug plan choice. Use Medicare.gov's Plan Finder with your actual prescription list.
2 months	Apply for Medigap (if going original-Medicare route). The 6-month Medigap guaranteed-issue window starts the day Part B begins.
Month of birth	Verify your Medicare card has arrived. Confirm coverage start date.

Critical detail on HSAs: Medicare enrollment of any kind disqualifies you from contributing to an HSA. If you contribute to an HSA, stop contributions the month before your Part A start date, accounting for any retroactive backdating. See the HSA Pre-Medicare category for details.

Step 5 — SEP enrollment action plan (delaying past 65)

If you have qualifying employer coverage at 65 and plan to delay:

Trigger	Action
6 months before retirement	Tell HR you're delaying Medicare. Request a written letter on letterhead confirming the plan was creditable for the entire period of delay. (You'll need this if Social Security ever questions your enrollment date.)
Day employment or coverage ends	Your 8-month SEP starts the next month. Mark the SEP end date on your calendar.
Within 60 days after coverage ends	Decide on Medigap (which has its own 6-month guaranteed-issue window starting when Part B begins).
Before SEP ends	Enroll in Parts A and B via SSA. Submit the CMS-L564 (employer's request for employment information) signed by HR confirming creditable coverage.

Action: Request the CMS-L564 signed letter from HR as soon as you decide to delay. Some HR departments take weeks to produce it; you don't want a last-minute scramble.

Step 6 — Part D and Medigap windows (separate from Parts A/B)

Part D has its own enrollment windows and its own late-enrollment penalty:

The Part D IEP runs alongside your Parts A/B IEP — same 7-month window.
If you have creditable drug coverage through your employer plan, you delay Part D the same way you delay Part B; the SEP coordinates.
If you go without creditable drug coverage for more than 63 days at any point after age 65, the Part D late penalty (1% per month, permanent) starts accruing.

Medigap (Medicare Supplement) has its own one-time guaranteed-issue window:

The Medigap window is 6 months, starting the first day of the month Part B becomes effective.
During this window, insurers cannot deny a Medigap policy or charge more based on health status.
Miss this window and Medigap underwriting applies; insurers can decline or charge dramatically more based on pre-existing conditions.

Action: If you're going original-Medicare with Medigap, line up your Medigap policy choice before your Part B start date so you can apply on day 1 of the 6-month window.

Print-friendly summary — the 5 dates to mark

Pull out a calendar and write these down for yourself:

IEP start: ______________________________
IEP end: ______________________________
Coverage end (if delaying via SEP): ______________________________
SEP end (if applicable): ______________________________
Medigap guaranteed-issue window end: ______________________________

If you're delaying past 65, you'll also want:

HR letter confirming creditable coverage received: ______________________________
CMS-L564 submitted: ______________________________

Primary sources

This checklist is published by NestPilot Foundation Inc. — a nonprofit (501(c)(3) filing in progress). It is free, primary-source-anchored, and not a substitute for personalized advice. If your situation is unusual (employer with fewer than 20 employees, COBRA-only coverage, retiree-only plan, working spouse with mismatched ages, multiemployer plan), consult a Medicare counselor or your employer benefits administrator.