how-to
How to Switch from Employer Insurance to Medicare
Last Updated: November 4, 2026
Quick Summary
To switch from employer insurance to Medicare, confirm your coverage end date with HR, then enroll in Part B through Social Security and submit Form CMS-L564 documenting your active employment coverage. If you retire or lose coverage, you get an eight-month Special Enrollment Period starting the month employer coverage ends.
- You can delay Part B without penalty while actively employed and covered by a group health plan.
- With 20 or more employees, the group health plan pays first and Medicare is secondary.
- The eight-month Special Enrollment Period starts the month your employer coverage ends.
- Ask HR for your last day of coverage, creditable drug coverage status, and a verification contact.
- Once you enroll in Medicare, you can no longer contribute to an HSA.
Table of Contents
- When You Can Switch from Employer Insurance to Medicare
- Medicare Special Enrollment Period for Employer Coverage
- Step-by-Step: How to Move from Employer Insurance to Medicare
- Avoiding the Medicare Part B Late Enrollment Penalty
- CMS Form L564: Request for Employment Information
- HSA, COBRA, and Spousal Coverage: Risks Most Guides Skip
- Comparing Employer Plan Costs with Medicare Costs
- Get Help Confirming Your Enrollment Window
- Frequently Asked Questions
When You Can Switch from Employer Insurance to Medicare
The best time to switch from employer insurance to Medicare depends on whether you or your spouse still works for the employer. If you are actively employed and covered by a group health plan, you can delay Medicare without penalty (Working past 65). People who stop working may enroll during a Special Enrollment Period; confirm the start month with the official source.
Missing a window can result in a late enrollment penalty; check the official rules for details.
Here are the two main paths:
- Still working, still covered: You can delay Part B. Your group plan stays primary.
- Retiring or losing coverage: You get an eight-month Special Enrollment Period.
The Social Security Administration administers enrollment, and the official Medicare enrollment guidance spells out these windows.
The 20-Employee Rule and Coordination of Benefits
Coordination of benefits decides who pays first. That answer hinges on employer size.
If your employer has 20 or more employees, the group health plan pays first and Medicare is secondary. You can delay Part B and keep your employer coverage as your main plan.
For smaller employers, Medicare may pay primary and the group plan second; check the official coordination-of-benefits rules for your situation.
Ask your benefits administrator which category your employer falls into. Get it in writing.
Medicare Special Enrollment Period for Employer Coverage
The Medicare Special Enrollment Period for employer coverage may allow enrollment in Part B after group coverage based on active employment ends. Check the official source for the current window length and eligibility rules.
Here is what the eight months look like in practice:
- It starts the month your employer coverage ends and runs eight full months.
- Enrolling late inside the window can still trigger a gap.
- Missing the window means waiting for the general enrollment period.
Coverage gaps are a risk to plan for; confirm Part B start timing with the official source before your group plan ends. Our guide on the Medicare Special Enrollment Period covers each scenario.
Step-by-Step: How to Move from Employer Insurance to Medicare
Moving from employer insurance to Medicare generally involves confirming your coverage end date, enrolling in Part B, submitting the required employment form, and deciding on drug and supplemental coverage.
Step 1: Confirm Your Coverage End Date with HR
Ask your benefits administrator for your exact termination date in writing.
Get three things from HR:
- The last day of active coverage
- Whether the plan is creditable coverage for drug purposes
- A contact name for future verification
That third item matters more than people expect. You will need employment verification later.
Step 2: Enroll in Part B and Submit CMS Form L564
Apply for Part B through Social Security using the application channels the agency makes available.
Then submit Form CMS-L564, the Request for Employment Information. Your employer fills out the employment section. You complete the rest.
This form is used to document group coverage through active employment; confirm its role with the official source.
Step 3: Decide on Part D and Supplemental Coverage
Original Medicare covers hospital and medical care, and many people consider supplemental or Medicare Advantage options to address out-of-pocket costs.
Drug coverage needs its own decision. Going without creditable prescription drug coverage for an extended period may affect Part D enrollment; check the official rules.
When you are ready to pick a supplement, our step-by-step Medigap selection guide walks through the comparison process. Start there before you commit.
Avoiding the Medicare Part B Late Enrollment Penalty
A Part B late enrollment penalty may apply when you go without creditable coverage after you were first eligible; check the official source for how it is calculated.
Two mistakes cause most penalties:
- Assuming COBRA counts as active employment coverage.
If you are unsure whether your situation is protected, our guide on avoiding the late enrollment penalty breaks down the rules and the exceptions. Read it before your window closes, not after.
CMS Form L564: Request for Employment Information
Form CMS-L564 is used to document group health plan coverage through active employment. Check the official source for how it is applied.
The form has two parts. You complete the personal information section. Your employer or former employer completes the employment section, including your coverage dates.
A few practical notes:
- Keep a copy for your records.
If your former employer is slow to respond, following up in writing is a reasonable step.
HSA, COBRA, and Spousal Coverage: Risks Most Guides Skip
Three situations trip up even careful planners: Health Savings Accounts, COBRA, and spousal coverage. Each has a trap generic guides skip, and each trap has a specific mechanism you can check before you enroll.
Health Savings Account: The Six-Month Lookback
Once you enroll in Medicare, you can no longer contribute to an HSA. You can still spend what is already there, and you can still pay Medicare premiums from the account tax-free in most cases. The trap is the timing.
Medicare Part A start dates can be retroactive in some cases. Because retroactive coverage may affect HSA contribution eligibility, check the official Medicare and IRS guidance on HSA rules before contributing.
HSA contribution eligibility can change once Medicare coverage begins, so review the official IRS guidance on timing before you apply.
COBRA Is Not Active Employment Coverage
COBRA is a continuation of the plan you had while working. Confirm with the official source whether it qualifies for any Special Enrollment Period.
That distinction matters because COBRA can feel like a safety net while Part B timing is still open. Confirm your Special Enrollment Period timing with the official source.
When weighing COBRA against Part B, review the official enrollment rules for your situation before electing either option.
Spousal Coverage: Test the Employer, Not the Marriage
If your spouse still works and you are covered under their group plan, you may be able to delay Part B based on their active employment. The coordination-of-benefits rules depend on employer size and active employment; check the official source for the current test.
Two details trip people up. First, the working spouse must be the one whose employment supports the coverage, a retiree covered as a spouse under a former employer's retiree plan is not active employment coverage. Confirm employer size and active-employment status in writing before you rely on any delay in Part B enrollment.
A Quick Pre-Enrollment Check
Before you file anything, confirm in writing your exact active coverage end date, whether the plan is creditable prescription drug coverage, the employer size for coordination of benefits, and any HSA contributions made around your intended Part B start.
Comparing Employer Plan Costs with Medicare Costs
Comparing costs is not apples to apples. Employer plans usually bundle drug coverage and cap out-of-pocket spending; Original Medicare does not. The useful comparison is total annual cost under each path, including the parts employer plans hide.
What You Actually Pay Under Each Path
| Cost factor | Employer plan | Original Medicare |
|---|---|---|
| Monthly premium | Payroll deduction, often shared with employer | Part B premium (income-related for higher earners) |
| Deductible | Set by plan | Part A deductible per benefit period; Part B deductible annually |
| Hospital stays | Copay per day or per stay | Part A deductible, then coinsurance after a set number of days |
| Doctor visits | Copay or coinsurance | 20% coinsurance after deductible, no cap |
| Drug coverage | Often included | Separate Part D plan with its own premium and deductible |
| Out-of-pocket maximum | Usually included | None under Original Medicare; only with Medigap or Medicare Advantage |
| Network | Employer-selected | You choose; Original Medicare accepted broadly, Advantage plans vary |
Part B premiums and deductibles change each year, and higher-income enrollees pay an income-related monthly adjustment amount. For current figures, our breakdown of Part B premium costs lists the numbers you need to run a real comparison against your employer plan.
The Three Numbers That Decide It
The decision often comes down to several factors beyond the premium alone.
First, your maximum out-of-pocket exposure. An employer plan caps what you can spend in a year; Original Medicare does not.
Second, your drug costs. Under Medicare, you need a standalone Part D plan or a Medicare Advantage plan with drug coverage, and the formulary may not include your prescriptions.
Third, your income. Part B and Part D premiums are income-related.
Run the Comparison in Four Steps
- Add up your employer plan's annual premium share, deductible, and expected copays for your actual care.
- Add up Medicare Part B premiums (including any income-related adjustment), a Part D premium, and either a Medigap premium or a Medicare Advantage premium.
- Add the worst-case out-of-pocket exposure under each path, the employer plan's out-of-pocket maximum versus Medicare's uncapped 20% coinsurance if you skip a supplement.
- Compare the two totals against your actual prescriptions and doctors, not a generic sample.
Comparing only the monthly premium can overlook out-of-pocket exposure, so review total annual costs before deciding.
When the Employer Plan Still Wins
If your employer subsidizes a large share of the premium and your income is above the Medicare premium adjustment threshold, the employer plan can be cheaper on a total-cost basis even after you turn 65. Outcomes vary by drug costs, income, and supplemental coverage, so run the comparison with your own numbers. Run the four steps with your own numbers before your coverage end date.
Get Help Confirming Your Enrollment Window
Confirm your coverage end date, review your Special Enrollment Period with the official source, and submit any required forms on time.
If you are still working past 65, our guide on enrolling while still employed answers the questions that come up most.
Your Medicare Agent Medicarehelpinfl provides guidance on Medicare eligibility and enrollment, including Original Medicare, Medicare Advantage, and supplemental plans.
Get started with Your Medicare Agent Medicarehelpinfl and confirm your enrollment window before your group coverage ends.
Frequently Asked Questions
Can I switch from employer insurance to Medicare while I am still working?
Yes, but the timing depends on your employer's size. Whether Medicare pays first or second depends on your employer's size and coverage rules; check the official coordination-of-benefits guidance for your situation. Confirm your plan's rules with your benefits administrator before you decide.
What is the Special Enrollment Period for employer coverage and how long does it last?
The Medicare Special Enrollment Period for employer coverage gives you a window to sign up for Part B after your job-based coverage ends. The enrollment window after employer coverage ends is set by official rules; check the official source for its current length and conditions. You will need proof of creditable coverage, often submitted with CMS Form L564, so request that form from your employer early.
How do I avoid the Medicare Part B late enrollment penalty when leaving my job?
Enroll during your Special Enrollment Period and submit CMS Form L564 signed by your employer. A Part B late enrollment penalty may apply if you go without Part B after you were first eligible; check the official source for how it is calculated. Getting the form in before your window closes is the simplest way to prevent the surcharge.
Do I need to enroll in Medicare if I have COBRA after leaving my job?
Whether COBRA affects Medicare late enrollment penalties depends on official rules; check the official source before deciding. If you keep COBRA instead of signing up for Medicare during your Special Enrollment Period, you may face a Part B penalty later. Compare the cost of COBRA with Medicare premiums and Part D options, and speak with a licensed agent before your eight-month window closes.
