Whether you should enroll at 65 or safely delay depends mostly on your employer's size. Here's how to decide — and how to avoid penalties — in plain English.
Quick answer
If you keep working past 65 with health coverage from a current employer of 20 or more employees, you can usually delay Medicare Part B without penalty until that job or coverage ends. If the employer has fewer than 20 employees, Medicare generally becomes primary at 65 and you should enroll on time. Many people still take premium-free Part A at 65 — but not if they want to keep contributing to an HSA. When you retire, an 8-month Special Enrollment Period lets you pick up Part B without penalty.
Turning 65 no longer means retiring. Many Californians keep working — and keep their employer health plan — well into their late 60s or 70s. The good news is that Medicare's rules allow for this. The catch is that the right move depends on details specific to your situation, and a wrong assumption can create a lifelong penalty or a coverage gap. This guide walks through how to think about it.
Almost everything about working past 65 comes down to the size of the employer providing your coverage — yours, or your spouse's, if you're on their plan through their current job.
If the coverage comes from current employment at an employer with 20 or more employees, the group health plan generally stays your primary coverage and Medicare would be secondary. In this situation, you can delay enrolling in Part B without a late-enrollment penalty for as long as that coverage continues. When the job or the coverage ends, a Special Enrollment Period lets you enroll then — penalty-free.
If the employer has fewer than 20 employees, Medicare generally becomes the primary payer once you turn 65, and the group plan pays secondary. That distinction matters a great deal: if you don't enroll in Part A and Part B on time, the plan may pay as though Medicare already covered its share — leaving you responsible for large bills. In these cases you usually should enroll in Medicare at 65. Always confirm how your specific plan coordinates with Medicare with your benefits administrator before deciding.
Most people qualify for premium-free Part A (hospital insurance) at 65 based on their work history. Because it usually costs nothing, many people enroll in Part A at 65 even while still working, where it can pay secondary to the employer plan.
There is one important exception: Health Savings Accounts (HSAs). Enrolling in any part of Medicare — including premium-free Part A — ends your eligibility to contribute to an HSA. You can still spend down an existing HSA, but new contributions must stop. If continuing to fund your HSA matters to you, you may want to delay Part A along with Part B.
HSA timing caution: When you eventually enroll in Part A after 65, coverage can be backdated up to 6 months (but never before your 65th birthday). To avoid a tax penalty on excess contributions, a common approach is to stop HSA contributions at least 6 months before you plan to start Medicare. Confirm your specific timing with a tax advisor.
To avoid a permanent Part D late-enrollment penalty, you need creditable prescription drug coverage — coverage at least as good as Medicare's — with no gap of 63 days or more. Most large employer plans are creditable, and your plan is required to send you an annual notice stating whether its drug coverage is creditable. Keep those notices; you may need to show them later when you enroll in a Part D or Medicare Advantage plan.
Coverage rules can hinge on plan-specific language, so treat this as a framework — not a final answer for your exact plan.
Whenever you decide to stop working — or your employer coverage ends — you move into a Special Enrollment Period (SEP): 8 months to enroll in Part B without penalty, and 2 months to pick up a Medicare Advantage or Part D plan. Enrolling before your employer coverage ends is the cleanest path, with no gap. Two things trip people up: COBRA and retiree coverage do not count as current-employer coverage, so they don't extend this window. For a full step-by-step walkthrough of that handoff, see our companion guide, Retiring after 65: moving from employer coverage to Medicare in California.
When you do come onto Medicare, you'll choose between the two main approaches — a Medicare Advantage plan, or Original Medicare paired with a Medigap policy and a Part D drug plan. We compare them in Medicare Advantage vs. Medicare Supplement, and our Medicare costs explained guide breaks down the 2026 numbers. If you're closer to 65 than to retirement, the Turning 65 in Southern California overview and our step-by-step turning 65 guide are good starting points.
Last reviewed: July 2026. Medicare rules and figures reflect 2026 and can change annually — confirm current details at Medicare.gov, and confirm HSA tax timing with a tax advisor. Educational information only, not individualized legal, tax, or medical advice.