What's the basic rule?
At 65 you become eligible for Medicare whether or not you've retired. Whether you should sign up for Part B right away depends on one question: do you have group health coverage based on current work, yours or your spouse's? If so, and the employer is large enough, you can usually delay Part B without a penalty and sign up later during a special enrollment period. If not, sign up during your Initial Enrollment Period to avoid gaps and penalties.
Most people get Part A with no premium, so many people who are still working take Part A at 65 even when they delay Part B. The main exception is if you contribute to a health savings account (see below).
Who pays first: does employer size matter?
When you have both Medicare and a job-based plan, federal rules decide which pays first (primary) and which pays second (secondary). The answer depends on how many people the employer has.
| Your situation | Employer size | Who pays first |
|---|---|---|
| 65 or older, coverage from your or your spouse's current job | 20 or more employees | The job-based plan; Medicare pays second |
| 65 or older, coverage from your or your spouse's current job | Fewer than 20 employees | Medicare; the job-based plan pays second |
| Under 65 with a disability, coverage from your or a family member's current job | 100 or more employees | The job-based plan; Medicare pays second |
| Under 65 with a disability, coverage from your or a family member's current job | Fewer than 100 employees | Medicare |
| End-stage renal disease, any group health plan | Any size | The group plan for the first 30 months of Medicare eligibility; then Medicare |
| Retiree coverage or COBRA | Any size | Medicare |
Small employers: if Medicare should pay first and you don't have Part B, your job-based plan may pay only what it would have paid as secondary coverage, leaving you with large bills. Many Oklahoma employers are small: family farms and ranches, local businesses, small-town clinics. If you or your spouse work for one, ask the benefits office in writing whether you need Part B at 65.
How do I sign up later? The 8-month special enrollment period
If you delayed Part B because you had job-based coverage from current work, you can sign up any time while you still have it, or during the 8 months after the job or the coverage ends, whichever comes first. You won't owe a late penalty.
- Get form CMS-L564 to your employer. The Request for Employment Information is where your employer confirms the dates you had group coverage based on current work. If the job was your spouse's, their employer completes it.
- Fill out form CMS-40B. This is the application for Part B. Pick the month you want Part B to start, usually the month your job-based coverage ends.
- Send both to Social Security. Sign up online at ssa.gov and upload the L564, or fax or mail both forms to your local Social Security office. If your employer can't complete the L564, call Social Security at 1-800-772-1213 to ask what other proof of coverage it will accept.
- Choose your other coverage. To join a Medicare Advantage or Part D plan after job-based coverage ends, you have 2 full months after the month it ends. Your 6-month Medigap open enrollment period starts when Part B begins.
What about COBRA and retiree coverage?
COBRA and retiree health plans are not coverage based on current work. They don't extend your time to sign up for Part B, and Medicare pays first when you have them. If you leave a job at 65 or older and take COBRA, sign up for Part B within the 8 months after your job ends; don't wait for COBRA to run out. Most retiree plans, including Oklahoma's EGID retiree plans, expect you to have Part A and Part B.
Can I keep my health savings account?
You can't contribute to a health savings account (HSA) once any part of Medicare starts, including Part A. For 2026, the HSA contribution limits are $4,400 for self-only coverage and $8,750 for family coverage, plus a $1,000 catch-up contribution if you're 55 or older; in the year Medicare starts, you can contribute only for the months before it begins.
- Part A can be backdated. When you sign up for Part A after 65, coverage usually starts up to 6 months earlier (but not before the month you turned 65). Stop HSA contributions, yours and your employer's, 6 months before you sign up for Medicare or start Social Security benefits, which enrolls you in Part A automatically.
- You can keep spending the HSA. Money already in the account can pay Part B, Part D and Medicare Advantage premiums and other qualified medical costs without tax. It can't pay Medigap premiums.
Drug coverage and the creditable coverage notice
Each year before October 15, an employer or union plan with drug coverage must tell you whether that coverage is "creditable," meaning expected to pay at least as much as Medicare's standard Part D coverage. If it is, you can delay Part D without a penalty. If it isn't, or you go 63 days or more in a row without creditable drug coverage after your Initial Enrollment Period, you may owe a Part D late penalty. Keep every notice. See Part D in Oklahoma.
What if I work for the State of Oklahoma, a school or a local government?
HealthChoice and the other health plans for Oklahoma public employees are offered through the Employees Group Insurance Division (EGID) of the Oklahoma Health Care Authority (OHCA; it moved from OMES in July 2024). EGID covers state, education and local government employees whose employer participates. Its retirement planning guide says:
- While you're working, you may contact Social Security to delay Part B, and your employer insurance is the primary payer.
- No penalty later. All insurance offered through EGID is creditable coverage, so you won't be assessed a penalty once your employer insurance ends.
- When you decide to leave, have your employer complete form CMS-L564 to show you had continuous group coverage from the time you became eligible for Medicare until your Part B starts.
- As a retiree, EGID's checklist says Medicare-eligible retirees and spouses must be enrolled in Part A and Part B, and if you delayed Part B you must contact Social Security to start it. If you're Medicare-eligible when you retire, your EGID retiree application, with the Medicare supplement or Medicare Advantage application, must reach EGID before your termination date.
EGID member services: 405-717-8780 or 1-800-752-9475. Retirees' choices are explained on state and teacher retirees and Medicare and HealthChoice Medicare retiree options compared.
School districts not in EGID, cities, counties, tribal governments, hospitals and private employers each set their own rules. Ask your benefits office three questions: does the plan pay first or second at 65, is its drug coverage creditable, and what does it require of retirees once they're eligible for Medicare?
TRICARE, FEHB and Indian health care
Civilian workers at Tinker Air Force Base and other federal workplaces in Oklahoma who have FEHB can generally keep it while they work and have their own choices about Part B. If you have TRICARE, you generally need Part A and Part B to keep TRICARE For Life once you're eligible for Medicare, with different rules while you or your spouse are on active duty. See veterans, TRICARE and military retirees. Care from IHS or a tribal health system isn't job-based coverage and doesn't let you delay Part B; see tribal health and Medicare.
Higher earners: IRMAA
If you're still earning a salary, check whether your income is high enough for an income-related surcharge on Part B and Part D. In 2026 it applies when modified adjusted gross income from two years earlier was above $109,000 for a single filer or $218,000 for a joint return. The brackets are cliffs, not marginal. Retiring counts as a life-changing event that can let you ask Social Security to use your newer, lower income with Form SSA-44. Try the IRMAA calculator.
Where can I get help?
Social Security handles Part A and Part B sign-up: ssa.gov or 1-800-772-1213. For how Medicare works with your job-based plan, call 1-800-MEDICARE (1-800-633-4227, TTY 1-877-486-2048). When you're ready to look at coverage for after you retire, see plans for your ZIP code, or request a call from a licensed insurance agent to go over plans from the companies they work with, at no cost to you. See also turning 65 in Oklahoma.
Sources
- Medicare.gov — Working past 65
- Medicare.gov — Which insurance pays first
- Medicare.gov — Avoid late enrollment penalties
- Social Security Administration — Sign up for Medicare Part B online, by fax, or by mail
- CMS — Form CMS-40B, Application for Enrollment in Part B
- CMS — Form CMS-L564, Request for Employment Information
- IRS — Publication 969, Health Savings Accounts and Other Tax-Favored Health Plans
- EGID (Oklahoma Health Care Authority) — Planning for your insurance needs (2025 edition): "If you decide to work past age 65"
- Employees Group Insurance Division (EGID, Oklahoma Health Care Authority) — Retirement checklist
- Employees Group Insurance Division (EGID, Oklahoma Health Care Authority) — State, education and local government employees
- Social Security POMS HI 01101.010, modified adjusted gross income for IRMAA
- TRICARE — TRICARE For Life
Frequently asked questions
Do I need Part B if I'm still working in Oklahoma at 65?
Not always. If you have health coverage from your own or your spouse's current job and the employer has 20 or more employees, that plan pays first and you can usually delay Part B without a penalty. If the employer has fewer than 20 employees, Medicare usually pays first, so you generally need Part B to avoid gaps. Ask your employer's benefits office how its plan works with Medicare.
I work for the State of Oklahoma or a school with HealthChoice. Do I need Part B at 65?
Not while you're working. The Employees Group Insurance Division (EGID), part of OHCA, says that if you work past 65 you may delay Part B, your employer insurance is the primary payer while you work, and because all EGID coverage is creditable you won't be assessed a penalty once it ends. When you leave, have your employer complete form CMS-L564 so you can sign up for Part B.
Can I keep contributing to my HSA after I turn 65?
Only if you are not enrolled in any part of Medicare. Once Part A starts, you can't contribute to an HSA. Because Part A can start up to 6 months before the month you sign up (but not before you turn 65), stop contributions 6 months before you sign up for Medicare or Social Security. You can still spend money already in the HSA, including on Part B, Part D and Medicare Advantage premiums.
Does COBRA count as employer coverage for Medicare?
No. COBRA isn't coverage based on current work, so it doesn't let you delay Part B. Your 8-month Part B special enrollment period starts when your job or job-based coverage ends, whichever comes first, not when COBRA ends. If you wait until COBRA runs out, you may face a gap and a lifetime late penalty.
What forms do I need to sign up for Part B after my job ends?
Form CMS-40B, the application for Part B, and form CMS-L564, the Request for Employment Information, which your employer fills out to confirm your group coverage based on current work. You can sign up online at ssa.gov (uploading the L564) or fax or mail the forms to your local Social Security office. If your employer can't complete the L564, call Social Security at 1-800-772-1213 to ask what other proof of coverage it will accept.
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