Working Past 65: How Medicare Works With Employer Insurance

One of the most significant Medicare choices you'll make is your decision to work beyond age 65 and have an employer health plan. Follow the rules and you can postpone Medicare without a penalty, while remaining on a superior employer health insurance plan. Bundle up right and you will have to deal with permanent monthly penalties, coverage gaps, or unforeseen tax bills due to problems with Health Savings Accounts. The first question in the decision tree is how many employees does your employer have? If your employer provides you with a plan with 20 or more employees, your employer plan will be the primary plan and Medicare is the secondary plan and you can delay Part B enrollment without penalties for late enrollment. Medicare is primary and generally, if your employer has less than 20 employees, you should enroll in Medicare Part B at 65 to avoid coverage gaps. The problem: When you sign up for any Medicare plan, including Medicare Part A that doesn't require a premium, your HSA contributions end. This is one of the options that many high-income individuals have to consider when deciding whether or not to retire while paying the same tax on their HSA contributions.

In this guide, you will learn about Medicare coverage choices after age 65, after 20 employees, the implications of HSA coverage, the dangers of COBRA and how to time your Medicare enrollment for 2026. Medicare.gov, CMS and IRS guidance provide information. 

The 20-employee rule: everything depends on this

The single most important factor for working past 65 is your employer's size. Medicare Secondary Payer (MSP) rules dictate which plan pays first – the 20-employee rule.

Federal law states that your employer must pay the premiums for your active status (even after you are Medicare eligible at age 65), and that the premiums are to be paid by the employer plan, not by Medicare coverage. Medicare is considered the "secondary payer. It is possible to avoid paying a late enrollment surcharge if you continue to be covered by your employer. The Special Enrollment Period is for 8 months after the period of coverage ends.

Medicare becomes the primary payer after age 65 for employers with less than 20 employees. Your small group plan becomes secondary plans and pays only the Medicare copayment. Most importantly, if you aren't signed up for Medicare Part B your employer plan might not pay for any services Medicare would have paid for, and that could leave you with gaps that are quite large.

If you are a small employer (fewer than 20 workers), and you require Medicare enrollment as a condition of your employee's continued coverage, you will need to cover them. Others may not. Confirm the employer's individual guidelines with an agreement in writing.

The 20 employees figure includes part-time and seasonal employees. The rules can be complicated for organisations that have more than one legal entity. Get your HR department to confirm in writing the employer plan's primary/secondary status.

When your spouse is covered by an employer (for example, if the employer provides coverage for your spouse), the size of the employer's workforce counts (20 employees), not yours.

For working past 65 specific enrollment scenarios, see our enrollment periods guide. 

The HSA pitfall

One of the biggest traps for people who work beyond age 65 is Health Savings Accounts (HSAs). After enrollment in Medicare (even for premium-free Part A), one may not make any further HSA contributions. This includes what your employer contributes to your HSA.

There is a 6% excise tax on excess HSA contributions (contributions made after Medicare enrollment) that will continue to accumulate until the money is withdrawn from the account. Penalty accrues on an annual basis.

A particularly tricky aspect is Medicare's 6-month retroactive enrollment for Part A. When you sign up for Medicare after age 65, your Part A coverage is also retroactive to the month you reach age 65, and is no longer backdated to the option of 6 months. This would include any HSA contributions that are made during those 6 retroactive months which will be considered excess contributions and subject to a penalty.

A 2026 example: Eric is 68 and is thinking of retiring in June 2026. He contributed the maximum amount to his HSA in January 2026 ($5,400). He applies for Social Security retirement benefits in June, which automatically enrolls him in Part A. Part A is backdated to December 1, 2025 (6 months before application). All of his $5,400 deposit is considered an excess contribution. He has to withdraw the money, pay income tax on the money earned and re-file paperwork.

The solution: avoid making HSA contributions for the previous 6 months prior to filing for Social Security or Medicare. Make sure to time your Medicare enrollment if you choose to contribute to your HSA. Other workers opt for Part A because of the value of premium-free Part A (which is an actual hospital benefit), even though many people delay enrollment in order to keep the HSA benefits going.

Even after losing eligibility to contribute, you can use HSA money for qualified medical expenses, such as some of the Medicare costs (Part A deductibles, Part B premiums, Part D premiums, copay). Only applies to contributions made post Medicare enrollment. 

The COBRA mistake

COBRA continuation coverage after losing employer-sponsored insurance is one of the most common and costly mistakes for those working past 65.

Many workers assume COBRA extends their Special Enrollment Period for delaying Medicare. It does not. Your 8-month SEP for Part B begins when active employment ends, not when COBRA expires. Taking COBRA without enrolling in Medicare Part B within the 8-month window from active employment ending triggers permanent late enrollment penalties.

A practical example: John retires June 30, 2025 at age 67. He elects COBRA on July 1, 2025, intending to use it through June 2026 to extend his coverage. His 8-month SEP began July 1, 2025 (the month after employment ended) and expires February 28, 2026. If he delays enrolling in Part B beyond February 28, 2026, he faces lifetime Part B late enrollment penalties.

COBRA does count as creditable prescription drug coverage for Part D purposes IF the coverage is verified as creditable. Always get this in writing from your employer or COBRA administrator.

Don't wait for COBRA to end before enrolling in Medicare Part B. Plan to be enrolled in Part B before the 8-month SEP expires.

For specific Special Enrollment Period details, see our SEP guide.

When to enroll in each part if working past 65

Working past 65 creates decision points for each Medicare part.

Part A (hospital insurance): If your employer has 20+ employees and you're contributing to an HSA, consider delaying Part A enrollment. If you're not contributing to an HSA, enroll in premium-free Part A at 65 for hospital coverage backup. If your employer has fewer than 20 employees, enroll in Part A at 65 to avoid potential coverage gaps. Once you receive Social Security retirement benefits, Part A enrollment is automatic and cannot be declined.

Part B (medical insurance): With 20+ employee coverage and good employer benefits, delay Part B until you lose coverage to avoid the $202.90 monthly premium. With fewer than 20 employees, enroll at 65 to prevent gaps. If your employer plan is high-deductible or expensive, even with 20+ employees, comparing the math of switching to Medicare Part B may make sense.

Part D (prescription drug coverage): Verify whether your employer drug coverage is creditable. If creditable, you can delay Part D without penalty. If not creditable, enroll in Part D at 65 to avoid the late enrollment penalty. When your employer coverage ends, you have 63 days to enroll in Part D without penalty if you had creditable coverage.

Medicare Advantage and Medigap: These options become available when you have Original Medicare (Parts A and B). With ongoing employer coverage, you typically don't need or want Medicare Advantage or Medigap. When transitioning from employer coverage to Medicare, you can choose between Original Medicare + Medigap (or Medicare Advantage during your SEP).

Practical scenarios for working past 65

Scenario 1: Working at 65 with good employer coverage from a 100-employee company. Most beneficiaries delay Part B and Part D, enroll in premium-free Part A unless contributing to HSA, and switch to Medicare when retiring. Use the 8-month SEP for Part B and 2-month SEP for Medicare Advantage or Part D.

Scenario 2: Working at 65 with employer coverage from a 10-employee company. Enroll in both Part A and Part B at 65 to avoid coverage gaps. Your employer plan becomes secondary to Medicare. Consider whether your employer plan still adds value or if dropping it for Medicare alone makes more sense.

Scenario 3: Working at 67 with HSA contributions and 25+ employee coverage. Continue working and contributing to HSA. Don't enroll in any Medicare part to preserve HSA contributions. Plan Medicare enrollment 6+ months before retirement application.

Scenario 4: Working at 70 with creditable employer coverage and no HSA. Enroll in premium-free Part A but delay Part B and Part D. Use the SEP to enroll in Part B and Part D when retiring.

Scenario 5: Returning to work after Medicare enrollment. If you re-enter employer coverage after Medicare enrollment, the employer plan becomes secondary if the employer has 20+ employees. You don't lose Medicare; the coordination of benefits adjusts. Verify with your benefits administrator.

For Medicare enrollment periods overview, see our enrollment periods guide.