Medicare Part B is not mandatory. It is a voluntary program, and you can choose to decline or delay enrollment without breaking any law. However, skipping Part B when you don’t have other qualifying coverage can leave significant gaps in your healthcare and trigger financial penalties that last the rest of your life.
Part B Is Voluntary, but You May Be Auto-Enrolled
Federal law treats Part B as an optional program that requires payment of a monthly premium. Nobody is legally required to sign up. That said, if you’re already receiving Social Security benefits at least four months before you turn 65, Medicare will automatically enroll you in both Part A (hospital coverage) and Part B. You’ll receive your Medicare card in the mail, and the Part B premium will be deducted from your Social Security check unless you actively opt out.
The same automatic enrollment applies if you’ve been receiving Social Security disability benefits for 24 months, or if you have ALS, in which case coverage begins as soon as disability benefits start. In all of these situations, you have the right to refuse Part B. You just need to follow through on declining it rather than letting it default to active.
What Part B Actually Covers
Part A covers inpatient hospital stays, skilled nursing facility care, hospice, and some home health services. If you only have Part A, everything outside a hospital or facility setting is essentially uncovered. Part B fills that gap by paying for doctor visits, outpatient procedures, lab work, durable medical equipment like wheelchairs and walkers, preventive screenings, vaccines, and annual wellness visits.
Without Part B, a routine visit to your doctor, an outpatient surgery, or even a diagnostic MRI would be entirely out of pocket. For most people, going without Part B means going without coverage for the majority of their day-to-day healthcare.
When Delaying Part B Makes Sense
The main reason to delay Part B without penalty is if you or your spouse are still working and covered by an employer group health plan. The key factor is the size of the employer. If the company has 20 or more employees, your employer plan is considered “primary” insurance, meaning it pays first and Medicare is secondary. In that scenario, you can safely delay Part B enrollment until the employer coverage ends, and you won’t face a late penalty.
If the employer has fewer than 20 employees, the rules flip. Medicare becomes the primary payer, and your employer plan only covers what Medicare doesn’t. In that case, delaying Part B could leave you underinsured because your small-employer plan expects Medicare to pay first.
Once your employer coverage ends (or you stop working, whichever comes first), you get a Special Enrollment Period of two full months after the month your coverage ends to sign up for Part B penalty-free. Missing that window pushes you into the next General Enrollment Period, which runs January through March each year, with coverage not starting until July.
The Late Enrollment Penalty
If you go without Part B and don’t have qualifying employer coverage during that gap, you’ll pay a permanent surcharge on your premium. The penalty is 10% added to your monthly premium for every full 12-month period you could have had Part B but didn’t. So if you waited two years, your premium goes up 20%. Three years, 30%. And for most people, this penalty lasts as long as you have Part B, which typically means the rest of your life.
With the 2025 standard Part B premium at $185.00 per month, a 20% penalty adds $37 per month, or about $444 per year, permanently. That cost compounds over decades of retirement.
How Part B Affects HSA Contributions
If you’re still working past 65 and contributing to a Health Savings Account, Medicare enrollment changes your eligibility. Once you enroll in any part of Medicare, including Part A, you can no longer make or receive tax-free HSA contributions. This is one reason some people who are still working delay both Social Security and Medicare enrollment: applying for Social Security automatically triggers Part A, which kills HSA eligibility.
There’s an additional wrinkle. If you apply for Part A after age 65, coverage is backdated up to six months from your application date or to the month you turned 65, whichever is more recent. Any HSA contributions you made during that retroactive period may exceed your annual limit and could be hit with a 6% excise tax. If you’re planning to keep contributing to an HSA past 65, the timing of your Medicare enrollment matters a great deal.
Help Paying the Part B Premium
If cost is the reason you’re considering skipping Part B, there are programs that can cover the premium for you. Medicare Savings Programs are state-administered and federally funded, and they pay Part B premiums (and sometimes deductibles and copays) for people with limited income.
- Qualified Medicare Beneficiary (QMB): Covers Part B premiums, deductibles, and copays. Individual income limit of $1,350 per month with resources under $9,950.
- Specified Low-Income Medicare Beneficiary (SLMB): Covers Part B premiums only. Individual income limit of $1,616 per month.
- Qualifying Individual (QI): Covers Part B premiums only. Individual income limit of $1,816 per month.
Income limits are slightly higher in Alaska and Hawaii, and some states use higher thresholds than the federal minimums. You apply through your state Medicaid office. These programs can make the difference between affording Part B and going without it.
One Exception: TRICARE Beneficiaries
If you’re a military retiree or dependent covered by TRICARE, Part B isn’t technically mandatory either, but it’s closely tied to your coverage. TRICARE for Life, the supplement available to military retirees over 65, requires enrollment in both Part A and Part B. Without Part B, you lose TRICARE for Life benefits. A Special Enrollment Period exists for TRICARE beneficiaries who initially declined Part B, allowing them to sign up outside the normal enrollment windows.
The Bottom Line on Skipping Part B
No law forces you to enroll. But the financial penalties for delaying without qualifying coverage are steep and permanent, the gap in healthcare coverage is significant, and programs exist to help if the $185 monthly premium is a barrier. For most people turning 65 without active employer coverage, enrolling in Part B on time is less a legal requirement and more a financial necessity.