Skip to content
Medicare guide · Employer coverage · 14 min read

Medicare and employer coverage — when you're an employee, when you're the employer.

About 20% of Americans 65+ are still working. The rules for how Medicare coordinates with employer health insurance are simple in theory and financially brutal when you get them wrong. The rules for self-employed retirees and small business owners are murkier still — but there's a specific tax deduction worth thousands per year that most people miss.

The single most important rule: 20 employees

This determines whether Medicare or the group plan is primary — and whether you can defer Medicare without penalty.

  • Group plan covers 20+ employees: Group plan is primary, Medicare is secondary. You can defer Part B without penalty. Federal Medicare Secondary Payer (MSP) rules require this.
  • Group plan covers fewer than 20: Medicare is primary, group plan is secondary. You almost certainly need to enroll in Medicare during your IEP. Skipping creates massive coverage gaps because the group plan only pays after Medicare would have paid.

Headcount is total employees company-wide for the prior calendar year, not just your office or department. Get this in writing from HR before making any deferral decision.

Scenario 1

You're an employee with employer coverage past 65

The most common scenario. You work for someone else, they offer health insurance, and you're approaching or past 65.

Step 1: Confirm employer size in writing

Ask HR or your benefits administrator in writing: "Does our company have 20 or more employees for Medicare Secondary Payer purposes?" Save the email or letter. The headcount that matters is total employees company-wide for the prior calendar year.

Step 2: Confirm creditable coverage status

For Part B deferral, the plan must be:

  • Based on you (or your spouse) actively working — NOT COBRA or retiree coverage
  • Covers you fully even without Medicare enrollment
  • Considered "creditable" by Medicare standards

For Part D deferral, your insurer is required to send you a "creditable coverage" letter each fall confirming the prescription drug coverage is at least as comprehensive as standard Medicare Part D. Save these letters. You'll need them when you eventually enroll in Part D to prove no late penalty applies.

Step 3: Decide on Part A

Part A is premium-free for most people (40+ quarters of Medicare-taxed work). Most people enroll at 65 even when deferring Part B — there's usually no downside. Exception: HSA contributors.

If you're contributing to a Health Savings Account, you cannot also be enrolled in Medicare Part A. Part A enrollment is retroactive up to 6 months when you sign up after your IEP. So if you intend to keep contributing to an HSA, defer Part A as well as Part B and stop HSA contributions at least 6 months before any Medicare enrollment to avoid IRS excess-contribution penalties.

Step 4: When the time comes — your 8-month SEP

When you eventually retire or lose group coverage, you have:

  • Part B SEP: 8 months from the month after your employment ends or your group coverage ends, whichever comes first. Use form CMS-L564 — your employer fills out the section confirming your creditable coverage dates.
  • Part D SEP: 2 months from the same trigger. Don't miss this — it's narrower than Part B.
  • Medigap window: in most states, your one-time 6-month Medigap Open Enrollment starts when your Part B becomes effective. Use this to lock in the cheapest Plan G or N carrier.

The COBRA trap

COBRA does NOT count as "current employer coverage" for Medicare deferral. If you turn 65 while on COBRA, the 8-month SEP doesn't apply. The Part B late-enrollment penalty clock keeps ticking. People lose 65th birthdays to this every year.

If you're on COBRA approaching 65, enroll in Part B during your IEP regardless of COBRA. You can keep COBRA as secondary, but Medicare must be primary.

The retiree-coverage trap

Retiree health insurance from your former employer is also not "current employer coverage" for Medicare purposes. If your retiree plan exists, it's typically designed to pay only what Medicare wouldn't pay — meaning you need Medicare as primary. Failing to enroll on time can leave huge gaps.

Scenario 2

You're the employer — self-employed, sole proprietor, or business owner

If you own the business, the rules depend on your structure and headcount. Plus there's a major tax deduction most self-employed retirees don't take.

Sole proprietor / 1099 contractor / freelancer

No employer group plan exists — you buy individual insurance (ACA marketplace, association plan, or similar).

  • Must enroll in Medicare at 65. Individual marketplace plans are NOT creditable for Part B deferral.
  • No 8-month SEP. You only have your IEP and the General Enrollment Period.
  • Drop your individual plan when Medicare starts. ACA premium tax credits are unavailable to anyone eligible for Medicare. Continuing the marketplace plan creates problems at tax time.

S-corp owner with employees

You own the corporation, you're employed by it, and the corporation has employees including you and (potentially) others.

  • If 20+ employees: group plan is primary; you can defer Part B (just like any employee).
  • If fewer than 20: Medicare is primary. You should enroll in Part B during your IEP even though you have group coverage.
  • 2% S-corp shareholders have specific rules: health insurance the corp pays for you must be reported as wages on your W-2 (Box 1), creating an above-the-line deduction on your personal 1040.

LLC owner (single-member, multi-member, or family)

Treatment depends on your tax election. Default for single-member LLCs is sole proprietor; LLCs can elect S-corp or C-corp treatment.

  • Single-member LLC (default): same rules as sole proprietor. Must enroll in Medicare at 65.
  • S-corp election: same as S-corp owner above — depends on employee headcount.
  • Multi-member LLC with employees: if 20+ employees and you have a group plan, MSP rules apply.

C-corp owner with health plan

The corporation deducts health insurance as a business expense; you receive it as a tax-free fringe benefit (subject to non-discrimination rules).

  • Same MSP rules apply based on headcount.
  • C-corps have flexibility S-corps don't — they can offer different health benefits to different employees, including more generous coverage to owners (within limits).
  • The plan must still meet ACA standards (no pre-existing exclusions, etc.).

The self-employed Medicare premium deduction (worth $1,000-$3,000/yr)

Most self-employed retirees miss this. It's worth real money.

If you're self-employed (sole proprietor, partner, or 2%+ S-corp shareholder) and you have net self-employment income, you can deduct your Medicare premiums (Parts A premium if applicable, B, D, IRMAA, and Medigap) as a self-employed health insurance deduction on Schedule 1 of your Form 1040 — above the line, no itemizing required, no AGI floor.

  • What's deductible: Part B premiums, Part D premiums, Medigap premiums, IRMAA surcharges, and Part A premium if you pay one. Your spouse's Medicare premiums also qualify if your spouse is also a Medicare beneficiary on your tax return.
  • Limit: capped at your net self-employment earnings for the year. If your business has a loss, no deduction.
  • Cannot double-dip: if you or your spouse have access to a subsidized employer plan (yours or theirs), the deduction is reduced by months when that coverage was available.
  • S-corp owners: the corporation pays the premiums, includes them as wages on your W-2, and you take the deduction on your personal return.
Real-world impact: a self-employed retiree with $50k net income paying $5,400/year in Medicare + Medigap + Part D premiums (typical Plan G + Part D + Part B base) deducts the full $5,400 above-the-line. At a 22% marginal federal rate plus state, that's roughly $1,200-$1,500 saved on taxes annually — for premiums you were paying anyway. Talk to a CPA who handles self-employed Medicare beneficiaries.
Scenario 3

Special cases

Spouse's employer coverage

If you're 65+ but your spouse is younger and still working at a company with 20+ employees, you can defer Part B and stay on their group plan as a dependent. Same MSP rules apply: their group plan is primary, Medicare secondary. When their employment ends, your 8-month SEP starts. Get the CMS-L564 form from their employer at that time.

Federal Employees Health Benefits (FEHB)

Federal retirees on FEHB have unique flexibility. FEHB is creditable coverage. You can suspend FEHB and use Medicare alone, or keep FEHB and use it alongside Medicare (FEHB is secondary in retirement, with catastrophic protections Medicare alone doesn't have). Many federal retirees keep both — the FEHB premium is competitive with Medigap, and the combination has remarkably low total OOP exposure.

TRICARE for Life (military retirees)

Military retirees on TRICARE who reach 65 transition to TRICARE for Life — which works as wraparound to Medicare. You MUST enroll in Part B to keep TRICARE for Life. After enrollment, Medicare pays first, TRICARE for Life picks up Medicare's deductibles, copays, and coinsurance. No Medigap needed; no Part D needed (TRICARE includes drug coverage).

VA health benefits

VA benefits are NOT a substitute for Medicare — they don't coordinate in the same way. Most veterans on VA care also enroll in Medicare to cover services VA may not provide quickly or close to home. VA doesn't enforce Medicare enrollment but doesn't compensate for not having it either. Most veterans should enroll in Part B at 65.

Quick decision framework

  1. Are you on an active group plan from an employer with 20+ employees? Defer Part B until you retire. Get the creditable-coverage letter in writing each year. Stop HSA contributions 6 months before any Medicare enrollment.
  2. Are you on COBRA, retiree coverage, or an individual marketplace plan? Enroll in Part B during your IEP. None of those count as creditable for deferral.
  3. Are you self-employed (sole prop / 1099 / single-member LLC)? Enroll at 65. Take the self-employed Medicare premium deduction on Schedule 1 — worth $1,000-$3,000/year for typical retirees.
  4. Do you own a business with 20+ employees? Same rules as any employee — defer if you have group coverage. The deduction may still apply for owner-employees with self-employment income.
  5. Are you a federal retiree, military retiree, or veteran? Special rules — FEHB / TRICARE for Life / VA each interact with Medicare differently. Generally enroll in Part B regardless; talk to your benefits administrator.
Run your numbers

What's the cheapest Medicare combination for your situation?

Once you've decided when to enroll, run the comparison to find the cheapest Plan G + Part D combo (or best MA-PD plan) for your zip, age, income, and medications.

Compare for $49
Related guides
Sources
· 42 U.S.C. § 1395y(b) — Medicare Secondary Payer statute
· CMS — Medicare Secondary Payer (MSP) Manual, Chapter 1 (Background and Overview)
· CMS — Form CMS-L564 (Request for Employment Information)
· IRS Publication 502 — Medical and Dental Expenses
· IRS Publication 535 — Self-employed health insurance deduction
· IRS Form 1040 Schedule 1 — Self-employed health insurance deduction line
· IRS Notice 2008-1 — 2% S-corp shareholder health insurance treatment
· OPM — FEHB and Medicare coordination
· DHA — TRICARE for Life eligibility and enrollment