Medicare enrollment timing — and the penalties that last forever
Of all the Medicare mistakes a federal retiree can make, the most expensive is also the most preventable: missing your enrollment window. The Part B late penalty is 10% for every year you delay — permanently, for as long as you have Medicare. And there’s a trap built specifically for feds: the retiree FEHB coverage you’re counting on does not let you delay Part B penalty-free. Here are the three enrollment windows, exactly how the penalties work, the fed-specific rule that catches people every year, and a calculator that shows what a late decision really costs.
1. The most preventable mistake
Medicare doesn’t send you a reminder before the clock starts. There’s no letter that says “enroll now or pay forever.” The responsibility is entirely yours, the deadline is tied to your 65th birthday, and the cost of missing it follows you for the rest of your life. That combination — no warning, permanent consequence — is why enrollment timing trips up so many otherwise careful retirees.
The good news is that the rules, once you know them, are completely manageable. There are exactly three windows to understand, one penalty structure, and a single fed-specific wrinkle that does most of the damage. Get those right and you’ll never think about it again. This guide is about timing — if you’re still deciding whether to take Part B at all as a fed with FEHB, start with the Part B decision guide, then come back here for the deadlines.
2. The three enrollment windows
Medicare gives you three ways in. Knowing which one applies to you is the whole game:
| Window | When | Who it’s for |
|---|---|---|
| IEP (Initial) | 7 months around your 65th birthday | Everyone — the default sign-up window |
| SEP (Special) | 8 months after current-employment coverage ends | Those who delayed Medicare due to active employer coverage |
| GEP (General) | Jan 1 – Mar 31 each year | The penalty-bearing fallback if you missed IEP and SEP |
Your IEP spans seven months: the three months before your birthday month, your birthday month, and the three months after. Enroll before your birthday month and coverage starts the month you turn 65; enroll during or after, and it starts the following month. The SEP protects people with current-employment coverage. The GEP is the safety net — but a costly one: since 2023, GEP coverage begins the first of the month after you enroll, which can leave you uninsured for months and saddle you with a penalty.
3. The Part B penalty: 10% forever
Here’s the rule that makes timing matter so much. If you don’t enroll in Part B when first eligible and don’t qualify for an SEP, your premium goes up 10% for each full 12-month period you could have had Part B but didn’t — and that surcharge is permanent, lasting as long as you’re enrolled in Medicare. It’s calculated on the base premium ($202.90 in 2026), regardless of your income.
Put numbers on it. Two years late is a 20% penalty — about $40.58 a month added on top of the premium. Seven years late is 70%, adding roughly $142 a month — turning a $202.90 premium into about $345. And because the penalty is a percentage of the base premium, it rises every year as premiums rise. Over a 20- or 25-year retirement, a delay that felt harmless at 65 quietly compounds into tens of thousands of dollars.
4. The fed trap: retiree FEHB doesn’t count
This is the single most important paragraph in this guide. Federal retirees naturally assume that because they have excellent FEHB coverage, they can safely delay Part B. For retirees, that assumption is wrong — and it’s expensive.
A Special Enrollment Period — the thing that lets you delay Part B without penalty — requires coverage from current, active employment. FEHB held as a retiree is not active-employment coverage, so it does not create an SEP and does not excuse you from the penalty. If you retire before 65, you must enroll in Part B during your seven-month IEP around your 65th birthday, full stop. Wait, relying on your retiree FEHB, and you’ll land in the GEP with a permanent penalty attached.
If you’re already a federal retiree when you turn 65, enroll in Part B during your Initial Enrollment Period. Your retiree FEHB is great coverage — but Medicare doesn’t treat it as the kind that lets you delay penalty-free. There is no SEP waiting for you.
5. Calculate your lifetime penalty
See what a delay actually costs. Set how long you’d be late on Part B, any months you’d lack creditable drug coverage for Part D, and how long you expect to be on Medicare. The calculator shows the permanent monthly penalties and the lifetime total.
Your delay
Part B penalty = 10% × full years late × $202.90 base. Part D penalty = 1% × months uncovered × the national base premium (~$37). Lifetime cost holds premiums flat, so the real figure is higher as premiums rise. Estimate only, not advice.
6. Working past 65: the SEP that protects you
The flip side of the retiree trap is a genuine advantage for those who keep working. If you stay in active federal service past 65 with FEHB, your FEHB is current-employment coverage — so you can delay Part B with no penalty and enroll later during an SEP that begins when you retire and runs eight months. Many feds in this position take premium-free Part A at 65 (it costs nothing and can coordinate with FEHB) while delaying Part B to avoid paying two premiums until they actually retire.
The crucial detail is that this protection ends at retirement. The moment you stop working, your eight-month SEP clock starts. Enroll within it and you’re penalty-free; let it lapse and you’re back to the GEP and the permanent penalty. So if you work past 65, calendar your retirement date and your SEP deadline together — the SEP is generous, but it is not forgiving of a missed deadline.
7. The Part D penalty
Prescription drugs have their own, separate penalty — but here federal retirees usually come out fine. The Part D late penalty is 1% of the national base beneficiary premium for each full month you go without “creditable” drug coverage (after a gap of 63 days or more), and like the Part B penalty, it’s permanent.
The reason it rarely bites feds: FEHB prescription drug coverage is creditable — at least as good as Part D — so every month you’re covered by FEHB counts as covered, and the penalty clock never runs. That’s also why most federal retirees don’t need a standalone Part D plan; their FEHB already does the job, and adding Part D would often just duplicate coverage. Keep the annual “creditable coverage” notice your FEHB plan sends — it’s your proof if anyone ever asks. For more on the drug side of coverage, see what Medicare doesn’t cover.
8. The spouse trap and Part A
Two final details that catch families:
The spouse trap. A spouse only gets an SEP if the FEHB-holding employee is still actively working. If you’re already retired and your spouse keeps working past 65 while covered under your retiree FEHB, the spouse does not qualify for an SEP — because retiree coverage isn’t current-employment coverage. In that situation, the working spouse must enroll in Part B at 65 to avoid the penalty, even though they’re still employed.
Part A is easy. Most federal retirees qualify for premium-free Part A (with 40 quarters of Medicare-taxed work), and premium-free Part A carries no late penalty — you can enroll anytime. The penalties in this guide are about Part B and Part D. Taking Part A at 65 is almost always the right move; the real decisions are about Part B timing and, separately, whether to keep FEHB alongside Medicare or weigh other options.
9. Frequently asked questions
What is the Medicare Part B late enrollment penalty?
It’s a permanent 10% surcharge on your Part B premium for each full 12-month period you were eligible for Part B but didn’t enroll, and you pay it for as long as you have Medicare. The penalty is calculated on the base Part B premium ($202.90 in 2026), not your income-adjusted amount. So two full years late means a 20% penalty — about $40.58 a month on top of the premium — and seven years late means 70%, adding roughly $142 a month for life. Because it never goes away and rises with future premiums, even a modest delay can cost many thousands of dollars over a long retirement.
What are the IEP, SEP, and GEP?
These are Medicare’s three enrollment windows. The Initial Enrollment Period (IEP) is the seven months around your 65th birthday — the three months before your birthday month, that month, and the three months after. The Special Enrollment Period (SEP) is an eight-month window after coverage from current active employment ends, available to people who delayed Medicare because they (or a working spouse) had employer coverage. The General Enrollment Period (GEP) runs January 1 to March 31 every year and is the fallback for anyone who missed both the IEP and an SEP; since 2023, GEP coverage starts the first day of the month after you enroll.
Does retiree FEHB let a federal retiree delay Medicare without penalty?
No — and this is the most expensive misunderstanding for federal retirees. A Special Enrollment Period requires coverage from current, active employment. FEHB held as a retiree does not count as active-employment coverage, so it does not give you an SEP and does not excuse you from the Part B late penalty. If you retire before 65, you must enroll in Part B during your seven-month Initial Enrollment Period around your 65th birthday, or you risk the permanent penalty. Only federal employees who keep working past 65 in active service get an SEP, because their FEHB is then current-employment coverage.
Can federal employees who work past 65 delay Medicare?
Yes. If you stay in active federal service past 65 with FEHB coverage, your FEHB counts as current-employment coverage, so you can delay Part B without penalty and enroll later during a Special Enrollment Period that begins when you retire and lasts eight months. Many federal employees take premium-free Part A at 65 and delay Part B until retirement to avoid paying two premiums while still working. The important catch is that this protection ends at retirement: once you’re a retiree on FEHB, the SEP clock is the eight months after you stop working, and missing it sends you to the penalty-bearing General Enrollment Period.
Do federal retirees need to worry about the Part D drug penalty?
Usually not, because FEHB prescription drug coverage is “creditable” — at least as good as Medicare Part D — so the months you’re covered by FEHB don’t count toward a Part D penalty. The Part D late penalty is 1% of the national base beneficiary premium for each full month you go without creditable drug coverage after a 63-day gap, and like the Part B penalty it’s permanent. Because FEHB keeps you creditable, most federal retirees don’t need a separate Part D plan and won’t owe the penalty. Keep the creditable-coverage notice your plan sends each year as proof.