When Should I Enroll in Medicare Parts A and B If I Still Work?

Do I have to sign up for Medicare when I turn 65 if I still have insurance through work?

No, not always. Medicare.gov says a person covered by a current worker’s job-based group plan may wait to enroll in Part B until employment ends or group coverage ends, whichever happens first, without a late-enrollment penalty.

The useful distinction is active employment versus coverage that merely continues. Active job-based group coverage is the condition that can support a delayed Part B decision. COBRA, retiree coverage, and other non-Medicare coverage are not substitutes for that condition when the Special Enrollment Period begins.

Medicare.gov describes the Initial Enrollment Period as seven months: the three months before the month you turn 65, your birthday month, and the three months after it. That period is the default enrollment window. Current job-based coverage creates a separate path, not an instruction to disregard Medicare paperwork indefinitely.

Part A needs its own review. Medicare.gov says people who do not owe a Part A premium may enroll at age 65 or later, but should check how enrollment affects their employer coverage and HSA eligibility. For readers comparing future health costs, this site also explains how Medicare coverage and payment questions can affect radiation therapy costs.

A three-part timing system

1. Identify the coverage. Confirm that it is a group health plan based on your or your spouse’s current employment.
2. Identify the payer order. Ask the plan whether Medicare would pay first or second at age 65.
3. Identify the next trigger. Record the earlier of the employment end date and group-coverage end date. That event starts the limited Part B enrollment window described by Medicare.gov and CMS.

Can I keep my employer health insurance and delay Medicare Part B?

Yes, you can keep qualifying employer group coverage and delay Part B while current employment continues, but the delay has to be coordinated with the end of work or coverage. According to Medicare.gov’s Working Past 65 guidance, the Special Enrollment Period lasts eight months and starts when work stops or insurance is lost, even if COBRA or another non-Medicare plan is chosen.

The sequence matters more than the label on the replacement coverage. Medicare.gov says that if someone wants Part B to start when job-based insurance ends, they can submit enrollment during the month before retirement; Part B begins the month after Social Security or the Railroad Retirement Board receives the completed forms. Missing the eight-month period can mean waiting for another enrollment period and may result in a Part B late-enrollment penalty that lasts as long as the person has Part B.

The HSA issue is the timing trap. IRS Publication 969 (2025) says the HSA contribution limit is zero beginning with the first month of Medicare enrollment. The IRS also says this rule applies to retroactive Medicare coverage, making contributions in that retroactive period excess contributions.

CMS states that when premium-free Part A is requested more than six months after age 65, Part A coverage is retroactive for six months. Medicare.gov advises people with HSAs to stop both employee and employer HSA contributions six months before retiring or applying for Social Security or Railroad Retirement benefits to avoid a tax penalty. This is a coordination problem, not a reason to make a rushed enrollment choice: the HSA payroll schedule, retirement date, Part A request, and benefit application date all need to be reviewed together.

Does my employer size affect whether I should enroll in Medicare?

Yes. Employer size can determine which coverage pays first, and that payment order can make a delayed enrollment far riskier at a smaller employer.

Medicare.gov says that for a person age 65 or older with coverage based on current employment, the group health plan generally pays first when the employer has 20 or more employees and Medicare pays second. When the employer has fewer than 20 employees and is not in a qualifying multi-employer group, Medicare pays first and the group plan pays second.

That distinction is not administrative trivia. Medicare.gov’s enrollment guidance warns that, because a company has fewer than 20 employees, job-based coverage might not pay for health services if the person does not have both Part A and Part B. The Medicare publication on coordination of benefits also notes that a multi-employer plan with at least one company employing 20 or more people is generally handled under the group-plan-pays-first rule.

Use the employer-size question as a verification step. Ask the benefits administrator whether the plan is a single-employer or multi-employer arrangement, whether Medicare is primary at age 65, and whether the plan requires Parts A and B before it pays. The written plan response matters because it turns a vague assumption into a documented coverage rule.