By the Kryder Cares Data Desk · Reviewed by Kris Kryder, licensed agent · Updated
Key points
- 20+ employees: the group plan generally pays first; Part B can usually wait.
- Under 20 employees: Medicare generally pays first — sign up on time.
- The 8-month Part B window starts when work or coverage ends, whichever is first.
- Stop HSA contributions 6 months before applying for Part A or Social Security.
Who pays first: the employer-size rule
When you have Medicare and another plan, one is primary (pays first) and the other secondary (pays only what’s left). For people 65 and older with group coverage from their own or a spouse’s current job, CMS’s rule turns on the employer’s size.
| Situation | Who pays first | What it usually means |
|---|---|---|
| 65+, employer has 20 or more employees | The group plan | You can generally delay Part B without a penalty |
| 65+, employer has fewer than 20 employees | Medicare | Sign up for Parts A and B on time, or the plan may not pay |
| Under 65 on disability, employer has 100 or more employees | The group plan | Ask the plan how it works with Medicare |
| Under 65 on disability, fewer than 100 employees | Medicare | Sign up on time |
Part A now, Part B later?
If Part A has no premium for you, many people take it at 65 even while working. CMS notes you can sign up for Part A at 65 or any time after.
The exception is a Health Savings Account. CMS says you and your employer should stop contributing 6 months before you retire or apply for Social Security, because Part A can be backdated up to 6 months and contributions after Medicare starts can mean a tax penalty. Kris isn’t a tax adviser; talk with your CPA about HSA timing.
The 8-month Special Enrollment Period
When you or your spouse stop working, or the job-based coverage ends — whichever happens first — you get an 8-month Special Enrollment Period to sign up for Part B with no late penalty. If you want Medicare to start the day your employer coverage ends, sign up the month before. Coverage starts the month after Social Security gets your forms.
You’ll file form CMS-40B to sign up for Part B if you already have Part A, along with an employer form showing you had job-based coverage while working. Kris can help you fill these out.
Ask your plan whether its drug coverage is creditable — it has to tell you. After it ends, you have 63 days to join Part D or a Medicare Advantage plan with drug coverage without a penalty.
COBRA and retiree coverage
COBRA lets you keep your former employer’s plan for a while, and it can cost up to 102% of the plan’s cost. For Medicare purposes it isn’t coverage from current work. Your 8-month window starts when the job ends, even if you choose COBRA, and once you’re 65 with Medicare, Medicare generally pays first. Waiting for COBRA to run out before signing up for Part B is one of the most common and costly mistakes.
Retiree coverage works the same way: it usually pays after Medicare and may not pay if you didn’t sign up for Parts A and B. Before joining any Medicare plan, ask the retiree plan whether joining would end your (or your family’s) coverage.
Self-employed, small employers and individual plans
If you’re self-employed or your coverage isn’t a group plan available to everyone at the company, ask whether it counts as an employer group health plan. If not, sign up for Medicare at 65 to avoid the Part B penalty. Marketplace coverage doesn’t let you delay Part B either, and once you’re eligible for Part A you can’t keep getting Marketplace premium help.
How Kris helps
Kris works with employees and with small employers across northwest Ohio, so she can look at both sides: what your group plan covers, whether it’s primary, and when Medicare makes more sense. Read her article on working past 65, see employee benefits, or compare Medicare Supplement options for when you retire. Our penalties guide explains what’s at stake.
Your next step
Have questions about your own situation? Contact Kris or schedule a no-cost meeting. You can also read more about Medicare Supplement (Medigap) and Medicare Advantage.
Sources
- CMS — Working past 65
- CMS — Which insurance pays first
- CMS — When can I sign up for Medicare?
- CMS — How do I sign up for Medicare?
- U.S. Department of Labor — COBRA continuation coverage
- CMS — Avoid late enrollment penalties
We do not offer every plan available in your area. Currently we represent 14 organizations which offer 119 products in your area. Please contact Medicare.gov or 1-800-MEDICARE to get information on all of your options. This is a proprietary website and is not associated, endorsed or authorized by the Social Security Administration, the Department of Health and Human Services or the Center for Medicare and Medicaid Services. This site contains decision-support content and information about Medicare, services related to Medicare and services for people with Medicare. If you would like to find more information about the Medicare program please visit the Official U.S. Government Site for People with Medicare located at www.medicare.gov.
This guide is general education, not a recommendation for any specific plan or policy. Figures were current as of October 19, 2026; plan details and government amounts change every year.