Comparing Employer Coverage vs Medicare

Key takeaway: Whether you can safely delay Medicare depends almost entirely on your employer's size — companies with 20 or more employees let you wait without penalty, but companies with fewer than 20 employees require you to enroll in Medicare right away or you'll accumulate permanent penalties.

What this helps you decide

• Whether your employer plan or Medicare pays primary — which one is the main insurance and which one fills in behind it
• Whether you're allowed to delay Part B enrollment without penalty, based on your employer's size and your situation
• When your 8-month Special Enrollment Period to sign up for Part B begins once you leave your job or lose employer coverage
• Whether coverage through a spouse's employer plan counts the same as your own employer's plan for Medicare delay purposes

Who this is for

• Someone who is 65 or older and still working, trying to decide whether to enroll in Medicare now or wait until they retire
• A person who recently turned 65 and is covered by a small employer (fewer than 20 employees) and may not realize Medicare must be their primary insurance
• Someone approaching retirement who wants to know exactly how long they have to sign up for Part B after their last day of work
• A 65-year-old covered by a working spouse's employer plan who needs to know whether that counts as valid coverage for delaying Medicare

Example results

Example 1 — Large employer, safe to delay Medicare. Maria is 66 years old and works for a company with 500 employees. She has a solid employer-sponsored health plan that covers her well, and she's not planning to retire for another two years. Because her employer has 20 or more employees, her employer plan pays primary and Medicare pays secondary. She can delay enrolling in Part B without any penalty. When Maria retires, she has an 8-month Special Enrollment Period starting the month after her active employment ends or her group coverage ends — whichever comes first. She needs to enroll in Part B during that window. If she does, she owes no penalty regardless of how many years she delayed. One important note: Maria should get a certificate of creditable coverage from her employer's HR department when she leaves. She may need it to prove her coverage was continuous when she enrolls.

Example 2 — Small employer, must enroll in Medicare immediately. Robert is 67 years old and works for a landscaping company with 12 employees. He has employer-sponsored health insurance and figured he'd just stay on it until he retired. But because his employer has fewer than 20 employees, Medicare is the primary payer — and since Robert never enrolled in Medicare Part B when he turned 65, he's been without his proper primary coverage for two years. That's two full 12-month periods of delay. His Part B penalty is 20% of the 2026 premium: 20% x $202.90 = $40.58 per month added permanently to his Part B premium. He'll pay $243.48 per month instead of $202.90 for the rest of his life. The penalty doesn't go away when he retires, and it increases if the base premium rises. Robert's best move now is to enroll immediately in Part B during the General Enrollment Period (January through March) to stop the penalty from growing further, then switch his employer plan to a supplement role or drop it altogether.

Example 3 — Covered by spouse's employer plan, large employer. Sandra is 65 and not working, but her husband David works full-time for a company with 80 employees. Sandra is covered under David's employer health plan. Because David's employer has 20 or more employees, Sandra can delay enrolling in Medicare Part B without penalty — the employer plan covers her as primary. When David retires or loses his employer coverage, Sandra's 8-month SEP begins. She has 8 months from that point to enroll in Part B without penalty. The key rule here is that coverage from a working spouse's employer plan at a qualifying-size company (20+) counts the same as your own employer's plan. If David's company had fewer than 20 employees, the situation would flip: Medicare would need to be Sandra's primary coverage, and any delay would accumulate penalties.

Sample scenarios

Scenario	Input	Result
Age 66, employer has 500 employees	Still working, good employer health plan, plans to retire in 2 years	Employer plan is primary. Can safely delay Part B. 8-month SEP begins when employment or coverage ends. No penalty if enrolled within that window.
Age 67, employer has 12 employees, 2 years late enrolling	Never enrolled in Part B, small employer, Medicare should have been primary	20% Part B penalty = +$40.58/mo permanently (based on 2026 premium of $202.90). Should enroll in next General Enrollment Period to stop penalty growth.
Age 65, covered by working spouse's employer (80 employees)	Not working, on spouse's group plan at large employer	Can delay Part B without penalty. 8-month SEP starts when spouse retires or coverage ends. Must enroll within that window.
Retired, COBRA for 18 months, no Medicare	Left job at 65, took COBRA instead of enrolling in Medicare	COBRA is not active employer coverage. SEP clock started when employment ended. Likely outside SEP now. Permanent Part B penalty applies for each 12-month delay period.

What to do next

• Find out exactly how many people your employer (or your working spouse's employer) has on payroll. Twenty is the cutoff that determines whether your employer plan or Medicare is primary. If you're close to that number, ask HR — part-time workers and seasonal employees often count toward the threshold differently depending on the plan.
• If you work for an employer with fewer than 20 employees and haven't enrolled in Part B yet, do it as soon as possible. Every additional month increases your permanent penalty. Enroll during the General Enrollment Period (January 1 through March 31) if you've missed your Initial Enrollment Period, and contact your State Health Insurance Assistance Program (SHIP) for help minimizing further damage.
• When you retire or lose employer coverage, mark your calendar for your SEP deadline — 8 months from the end of employment or coverage. Do not wait until month 7 or 8. Enrollment paperwork can take time, and missing this window by even a day puts you back into General Enrollment Period territory with a penalty.
• Ask your HR department for a creditable coverage certificate when you leave. This document shows Medicare that your employer coverage was continuous and legitimate. Without it, you may face delays or requests for proof when you try to enroll without a penalty.

Key facts

• For employers with 20 or more employees, the employer plan pays first and Medicare pays second. You are allowed to delay Part B enrollment while that active coverage is in place, and you will not face a late enrollment penalty as long as you enroll within your Special Enrollment Period after coverage ends.
• For employers with fewer than 20 employees, Medicare pays first — you must enroll in Part B when you are first eligible or face permanent late enrollment penalties. Staying on the small employer's plan without enrolling in Medicare does not protect you from penalties.
• After leaving employer coverage from a company with 20 or more employees, you have an 8-month Special Enrollment Period to sign up for Part B without penalty. This window begins the month after employment ends or group coverage ends, whichever comes first — not when COBRA runs out.

Related decisions

• COBRA vs. Medicare — Understand why COBRA doesn't count as employer coverage for Medicare purposes and how it can trigger permanent penalties if used as a Medicare substitute.
• Special Enrollment Period — See all the life events that open a penalty-free Medicare enrollment window, and how long each window lasts.
• When should I sign up for Medicare? — Walk through the full enrollment timing decision based on your age, employer size, and coverage situation.
• HSA compatibility — If you're delaying Medicare to keep employer coverage, learn how that affects your ability to contribute to a Health Savings Account.