Medicare and employer coverage in Hawaii — coordination of benefits

When you have both Medicare and employer health coverage, the rules about which one pays first — and whether you should have both — depend almost entirely on your employer's size. Get the coordination wrong and you can face surprise bills, lifetime penalties, or pay for coverage you don't need.

Primary vs. secondary payer — the foundational concept

When two health plans cover the same person, one is the primary payer (pays first) and one is the secondary payer (pays whatever the primary didn't cover, up to its own limits). Federal law — specifically the Medicare Secondary Payer rules — determines which is which.

The basic rule for working-age Medicare beneficiaries:

The "20 employee" rule explained in detail

This is the single most important number for Hawaii residents working past 65. The threshold is based on whether your employer has 20 or more employees on at least 50% of typical business days in the previous calendar year. It includes:

• Full-time and part-time employees
• Employees of related companies (controlled groups under IRS rules)
• Employees in all locations, not just Hawaii

If your employer is right at the threshold or fluctuates, ask HR for a written statement. The rule is determined annually, so an employer that crosses the line one year may shift the next.

The COBRA myth — why COBRA is not creditable for Medicare

One of the most expensive misunderstandings: COBRA does not count as creditable employer coverage for Medicare delay purposes. Once you turn 65 and lose active employer coverage:

• Your Special Enrollment Period for Part B starts the month employment ends, not when COBRA ends
• If you wait until COBRA expires (typically 18 months later) to enroll in Part B, you'll likely owe a lifetime late enrollment penalty
• Medicare will be primary while you're on COBRA, so COBRA only pays a small share of bills

The right move for most Hawaii residents losing employer coverage at or after 65 is to enroll in Medicare immediately and skip COBRA — or use COBRA only as supplementary coverage during the brief transition.

What counts as "creditable coverage" for Medicare delay

To delay Medicare without penalty, your alternative coverage must be creditable. The bar is different for Part B than for Part D:

Part B: "Active employer group health plan"

Coverage must be:

• Through current active employment (yours or your spouse's)
• From an employer with 20+ employees (otherwise Medicare is primary)
• True health insurance, not a discount card or HRA-only arrangement

What does NOT count: COBRA, retiree-only plans, individual market coverage, TRICARE alone (though TRICARE has its own rules — see our TRICARE guide), VA health care alone.

Part D: "Creditable prescription drug coverage"

Coverage must pay at least as much as standard Medicare Part D. Most large-employer plans qualify — your employer is required to give you a creditable coverage notice annually. Keep these notices. See our Part D creditable coverage guide for details.

Should you enroll in Part A at 65 even if working?

Part A is free for most people (those with 40+ work quarters). The standard advice has been "yes, enroll in Part A — it's free and it doesn't hurt." But this advice is wrong for HSA contributors. See our dedicated HSA and Medicare guide.

For non-HSA participants, enrolling in free Part A at 65 is generally a good move:

• It's free if you qualify
• It can pay secondary on hospital stays, reducing your costs
• It's a backup if employer coverage has a gap

For HSA contributors, you typically should not enroll in Part A while still contributing.

Hawaii-specific coordination situations

EUTF retirees still working part-time

If you retired from a Hawaii state, county, or DOE job and have EUTF retiree coverage, then took a part-time job, your EUTF retiree plan is generally not "active employment" for Medicare purposes. EUTF retiree coverage assumes Medicare is primary at 65. See our EUTF retiree guide.

Federal employees in Hawaii (FEHB)

FEHB and Medicare have specific coordination rules. Active federal employees can typically delay Part B; postal retirees moved into PSHB in 2025 with new Medicare requirements. See FEHB and PSHB coordination.

Native Hawaiian Health Care Systems

If you receive care through a Native Hawaiian Health Care System (NHHCS), Medicare is generally primary and NHHCS provides services not covered by Medicare or covers Medicare cost-sharing for eligible Native Hawaiian beneficiaries. See NHHCS coordination.

Self-employed in Hawaii

If you're self-employed at 65 and on the individual marketplace, that's not "active employer coverage" — it's individual coverage. You should enroll in Medicare at 65 to avoid penalties. The marketplace's premium subsidies typically end at 65 anyway because you become Medicare-eligible.

Action steps for Hawaii kupuna nearing 65

1. Confirm your employer size in writing — get HR to state whether the employer has 20+ employees for Medicare coordination purposes. Save the letter.
2. Get your annual creditable coverage notice for Part D — your employer is required to send this. Save them — you'll need them when you eventually enroll in Part D.
3. If your employer has fewer than 20 employees, enroll in Part B at 65 regardless of whether you're keeping employer coverage.
4. If you contribute to an HSA, see our HSA and Medicare guide before deciding on Part A enrollment.
5. Plan your retirement timing — your Special Enrollment Period for Part B starts when active employment ends. See our Part B SEP guide.
6. Talk to a licensed agent — coordination is genuinely complex and worth getting right. Find a Hawaii Medicare agent for free help.