Medicare at 65 has a reputation a bit like a smoke alarm: it’s not “mandatory” in the handcuff-y legal sense, but ignoring it can get loud, expensive, and oddly smoky at the worst possible time.
So, is Medicare mandatory? Sometimes you’re automatically enrolled. Sometimes you can delay. Sometimes you can decline. And sometimes you can do all of the abovethen accidentally earn yourself a lifelong premium surcharge for the thrilling sport of “paperwork procrastination.” Let’s keep you out of that league.
Is Medicare mandatory?
Usually, no. Most people are not legally required to enroll the moment they’re eligible. But Medicare has a “soft mandatory” vibe because:
- Penalties can be long-lasting (often for as long as you have the coverage).
- Other coverage may stop playing nice once you’re eligible for Medicare (hello, coordination-of-benefits rules).
- Some programs effectively require Parts A and B to keep benefits (TRICARE is a big one).
- Marketplace subsidies can disappear once you’re eligible for premium-free Part A, and you may even have to repay subsidies if you keep taking them.
Bottom line: Medicare isn’t always “mandatory,” but the rules around delaying and declining are strictespecially for Part B and Part D.
Medicare in 60 seconds: Parts A, B, C, and D
- Part A (hospital insurance). Often premium-free if you (or a spouse) worked long enough paying Medicare taxes.
- Part B (medical insurance). Monthly premium required; late enrollment penalties are common.
- Part C (Medicare Advantage). Private plans that replace Original Medicare (A & B) and usually include drug coverage.
- Part D (prescription drugs). Standalone drug plans or included in many Advantage plans; late penalties apply.
When you can enroll (and why timing matters)
Initial Enrollment Period (IEP): your first big window
Your Initial Enrollment Period is a 7-month window: it starts 3 months before the month you turn 65, includes your birthday month, and ends 3 months after that month.
Special Enrollment Period (SEP): the “I’m still working” exception
If you have health coverage from current employment (yours or your spouse’s), you may be able to delay Part B without penalty. The key idea is: the coverage must be tied to active work, not “I used to work there and they still like me.”
General Enrollment Period (GEP): the “oops” window
Missed your IEP and don’t qualify for an SEP? The General Enrollment Period runs January 1–March 31 each year. Coverage typically starts the month after you enroll, and penalties may apply.
Delaying or declining Medicare: what’s allowed vs. what’s smart
Part A: usually safe, sometimes strategic to delay
Many people enroll in premium-free Part A at 65 because it often costs $0 and can help as secondary coverage. But there are two common reasons people delay or decline Part A:
- You contribute to an HSA. Once you’re enrolled in any part of Medicare, you generally can’t contribute to an HSA. Also, enrolling in premium-free Part A later can trigger a retroactive start (up to 6 months), which can make recent HSA contributions “excess” contributions.
- You have to pay a premium for Part A. If you don’t qualify for premium-free Part A and you delay, you can face a penalty.
Part A late enrollment penalty (only if you must pay for Part A)
If you have to buy Part A and you don’t sign up when first eligible, your monthly premium may go up 10%, and you’ll generally pay that penalty for twice the number of years you delayed.
Part B: the penalty magnet
Part B is where most “Wait… why is my premium higher?” stories begin.
Part B late enrollment penalty
If you don’t sign up for Part B when you’re first eligible and you don’t qualify for a Special Enrollment Period, you typically pay an extra 10% for each full 12-month period you could have had Part B but didn’t. For most people, you pay this as long as you have Part B.
Concrete example (because math hurts less with coffee): If you wait 2 full years to enroll and don’t qualify for an SEP, that’s a 20% penalty. Using the 2026 standard Part B premium of $202.90, a 20% penalty adds $40.58, for a total of $243.48 (rounded to the nearest $0.10 by Medicare).
When delaying Part B can be reasonable
Delaying can make sense if you have employer coverage based on current employment and the employer plan will remain primary. But be careful:
- COBRA and retiree coverage generally don’t count as coverage based on current employment for Part B SEP purposes.
- VA coverage generally doesn’t qualify you for the Part B SEP. You can keep VA benefits, but delaying Part B can still trigger penalties later.
- Employer size matters. Medicare coordination rules often depend on whether the employer is treated as having 20+ employees (Medicare secondary) versus fewer than 20 (Medicare often primary).
Part D: the “63-day rule” people forget
You don’t have to enroll in Part D the moment you get Medicareif you have other creditable prescription drug coverage. But if you go 63 days or more without creditable drug coverage after your eligible window, you may face a late enrollment penalty.
Part D late enrollment penalty (how it’s calculated)
Medicare generally charges 1% per uncovered month times the national base beneficiary premium (which can change each year). That monthly penalty is added to your Part D premium for as long as you have Medicare drug coverage.
Example: If you go 18 months without creditable drug coverage, your penalty is roughly 18% of the base premium. Using the 2026 national base beneficiary premium of $38.99, 18% is about $7.02, which Medicare rounds to the nearest $0.10 (so about $7.00)added every month on top of your plan premium.
The biggest “delay/decline” traps (and how to avoid them)
Trap #1: “I’ll just do COBRA and enroll later.”
COBRA can be helpful for bridging coverage, but it usually doesn’t protect you from Part B penalties like active employer coverage does. If you stop working, your Part B SEP clock can start ticking whether or not you elect COBRA. Translation: COBRA is not a magical “pause button” for Medicare rules.
Trap #2: “Retiree coverage counts like employer coverage, right?”
Retiree coverage is often valuablebut it’s not the same as coverage based on current employment. Many people learn this only after a penalty letter arrives, like an unwanted subscription you forgot to cancel.
Trap #3: “I have a Marketplace plan, I’ll keep it.”
You can have Marketplace coverage before Medicare starts, but once you’re eligible for premium-free Part A, you generally won’t qualify for Marketplace savings. If you keep getting premium tax credits when you shouldn’t, you may have to repay them at tax time. Also, Marketplace coverage doesn’t end automaticallyso you have to actively manage the transition.
Trap #4: “I only use VA, so I don’t need Part B.”
VA health care can be excellent, but it generally doesn’t give you the same enrollment protections as an active employer plan. If you want the option to use non-VA providers later (or you move, or priorities change), delaying Part B can mean waiting for the GEP and paying penalties.
Trap #5: “I’ll keep my HSA contributions going until the day I enroll.”
If you enroll in premium-free Part A after 65, Medicare can start your Part A coverage retroactively (up to 6 months, but not earlier than your eligibility month). That retroactive coverage can make HSA contributions during that period ineligible. The practical move many advisors recommend is to stop HSA contributions well before your Medicare start date.
Declining Medicare: yes, but do it correctly
You can decline some parts of Medicare, but the “how” depends on your situation:
- If you’re automatically enrolled (often because you’re already receiving Social Security benefits), you may have to actively refuse Part B if you don’t want it.
- If you want to keep contributing to an HSA, you typically need to avoid enrollment in Medicare (including Part A), which can be complicated if you’re already collecting Social Security.
- If you drop Part B later, you can lose related coverage (like Medicare Advantage plans) and you may face late penalties if you re-enroll.
Pro move: Before you decline anything, get crystal-clear on whether you have “creditable coverage” for (1) medical services (Part B rules) and (2) prescriptions (Part D rules). Those are separate questions with separate consequences.
A quick decision checklist (print this mentally)
- Am I still working? If yes, is my coverage tied to current employment (mine or spouse’s)?
- How big is the employer? If it’s small, Medicare may need to be primary.
- Do I contribute to an HSA? If yes, plan the Medicare start date carefully (watch retroactive Part A).
- Do I have creditable drug coverage? If not, think Part D or an Advantage plan with drug coverage.
- Do I have TRICARE/CHAMPVA? These often expect timely Part A and Part B enrollment.
- Am I relying on COBRA, retiree coverage, VA, or Marketplace coverage? These are common “SEP misunderstandings.”
- Did I save proof? Keep employer forms and creditable coverage notices like they’re concert tickets.
Conclusion: Medicare isn’t mandatory, but the penalties are very committed
Medicare gives you choicesenroll, delay, declinebut it also rewards people who play by its timing rules. If you’re eligible and unsure, the safest approach is to decide intentionally: confirm whether your current coverage qualifies you to delay, map your enrollment windows, and document everything.
Because the only thing worse than paying a late penalty is paying it while thinking, “Wow, I really did this to myself.”
Real-life-ish Experiences: What People Learn the Hard Way (and Sometimes the Funny Way)
1) The “I’m Still Working” Planner. Maria turned 65 and kept working with solid employer insurance. She assumed she could skip Medicare entirely, but she did one smart thing: she asked HR whether the coverage was considered based on current employment and whether the employer was treated as large enough for Medicare to be secondary. HR confirmed it, and Maria delayed Part B without penalty. Later, when she retired, she enrolled during her Special Enrollment Period with the right documentation, and everything went smoothly. Her review of the process: “Shockingly boring. Highly recommend.”
2) The COBRA Bridge That Became a Trap. Dan retired at 65 and grabbed COBRA, thinking, “Greatsame doctors, same card, I’ll enroll in Medicare when COBRA ends.” Unfortunately, COBRA didn’t protect him from Part B timing the way active employment coverage would. Months later, he discovered his Part B Special Enrollment Period didn’t magically “wait” for COBRA to finish. He ended up enrolling later than he should have and learned what a late enrollment penalty looks like in real life: not dramatic, not exciting, just an extra cost every month that makes you sigh loudly at the mailbox.
3) The HSA Super-Fan With a Calendar Problem. Priya loved her HSA. She maxed it out, invested it, and treated it like a retirement Swiss Army knife. She delayed Medicare so she could keep contributing, which can be a valid strategyuntil she enrolled after 65 and learned that Part A can be retroactive for up to six months. Her payroll contributions during that retroactive window suddenly became “ineligible,” creating a scramble to correct excess contributions before tax filing deadlines. Priya’s takeaway: “Medicare is like a time traveler. If you’re doing HSAs, plan like it is.”
4) The VA-Only Minimalist Who Wanted Options Later. Robert used VA care for years and felt set. He skipped Part B because he didn’t see the point of paying a monthly premium. Then he moved to be closer to family, and the nearest VA facility was much farther away than expected. Suddenly, having broader access to non-VA providers mattered. He discovered that enrolling in Part B later could mean waiting for the General Enrollment Period and possibly paying a late penalty for as long as he had Part B. He still values VA carebut now he treats Medicare Part B as “option insurance.”
5) The TRICARE Family Who Didn’t Want Surprises. Elaine and her spouse had TRICARE and thought Medicare would be optional. They learned early that keeping TRICARE benefits when Medicare-eligible typically requires having both Part A and Part B. They enrolled on time, avoided penalties, and described the experience as: “Annoying, but in the way flossing is annoyingbetter than the alternative.”