Medicare Part B is not mandatory. You can decline it or drop it at any time. However, choosing to go without Part B can trigger a permanent late enrollment penalty if you don’t have qualifying coverage through an employer, and it can cause you to lose other benefits like TRICARE. So while no law requires you to enroll, skipping Part B without a valid reason carries real financial consequences.
Why It Feels Mandatory
If you’re already receiving Social Security or Railroad Retirement Board benefits at least four months before you turn 65, Medicare automatically enrolls you in both Part A (hospital coverage) and Part B (outpatient and doctor coverage). You’ll receive a welcome packet in the mail with your Medicare card, and unless you actively opt out, your Part B premiums start getting deducted from your Social Security check. The standard premium is $185 per month in 2025, rising to $202.90 in 2026.
People with disabilities follow a similar path. After 24 months of receiving Social Security disability benefits, you’re automatically enrolled in both Part A and Part B. Again, you can decline Part B, but the default is enrollment.
If you’re not receiving Social Security or Railroad Retirement benefits when you become eligible, you won’t be automatically enrolled. You’d need to sign up on your own during your initial enrollment period, which is the seven-month window surrounding your 65th birthday.
How to Decline or Drop Part B
If you’ve been automatically enrolled and don’t want Part B, you need to follow the instructions in your Medicare welcome packet and send your Medicare card back. Keeping the card counts as accepting coverage, and you’ll owe premiums. To drop Part B after you’ve already had it, you submit a written, signed request to Social Security. Your coverage ends at the end of the month following the month you file. So if you file on April 5, coverage ends May 31.
When Skipping Part B Makes Sense
The main scenario where delaying Part B carries no penalty is when you or your spouse are still working and covered by an employer group health plan. The key detail: the coverage must be through a current employer, and it must qualify as group health plan coverage as defined by the IRS. Retiree health plans, COBRA, and individual marketplace plans do not count.
There’s no firm rule about employer size in the research, but the general guidance from Medicare is to ask your insurance provider directly whether your coverage qualifies. If it doesn’t, you should sign up for Part B at 65 to avoid penalties. Once you or your spouse stop working (or lose that group coverage), you get a Special Enrollment Period to sign up for Part B without penalty.
The Late Enrollment Penalty
This is where the “voluntary” nature of Part B gets teeth. If you go without Part B and don’t have qualifying employer coverage during that gap, you’ll pay a 10% premium surcharge for every full 12-month period you were eligible but not enrolled. Two years without coverage means a 20% penalty on top of your standard premium. Three years, 30%.
The penalty is permanent. You’ll pay it every month for as long as you have Part B, which for most people means the rest of their life. On a 2025 base premium of $185, a 20% penalty adds $37 per month, or about $444 per year, indefinitely. That cost compounds as the base premium rises each year.
If you miss your initial enrollment window and don’t qualify for a Special Enrollment Period, you can only sign up during the General Enrollment Period, which runs January 1 through March 31 each year. Coverage starts the month after you enroll.
TRICARE Requires Part B
For military retirees and their dependents, Part B is effectively mandatory. If you’re eligible for both TRICARE and Medicare Part A, you must have Medicare Part B to keep TRICARE coverage in most cases. This applies to TRICARE For Life, the supplement that covers costs Medicare doesn’t pick up. Without Part B, you lose TRICARE entirely, even if you have employer-sponsored group coverage.
If you dropped Part B or missed your enrollment window, you can sign up during the General Enrollment Period. Your Part B and TRICARE For Life coverage will start the first day of the month after you enroll, but you may still face the late enrollment penalty on your Part B premium.
Higher Premiums for Higher Incomes
The standard Part B premium applies if your modified adjusted gross income is $106,000 or less as an individual, or $212,000 or less filing jointly (2025 figures). Above those thresholds, you pay an income-related surcharge on top of the standard premium.
- Individual income $106,001 to $133,000 (joint $212,001 to $266,000): $259 per month total
- Individual income $133,001 to $167,000 (joint $266,001 to $334,000): $370 per month
- Individual income $167,001 to $200,000 (joint $334,001 to $400,000): $480.90 per month
- Individual income $200,001 to $499,999 (joint $400,001 to $749,999): $591.90 per month
- Individual income $500,000 or more (joint $750,000 or more): $628.90 per month
These surcharges are based on your tax return from two years prior. A one-time income spike, like selling a home or taking a large retirement distribution, can temporarily push you into a higher bracket. You can appeal if your income has since dropped due to a life-changing event like retirement, divorce, or the death of a spouse.
The Bottom Line on “Mandatory”
No one will fine you or take legal action for declining Part B. But the system is designed so that opting out without qualifying employer coverage results in a permanent financial penalty when you eventually do enroll. For military retirees, skipping Part B means losing TRICARE. And for the majority of people turning 65 while collecting Social Security, enrollment happens automatically unless they take steps to stop it. Part B is technically optional, but for most people, the cost of not having it is higher than the cost of keeping it.