Intro
At 65, every federal retiree faces a decision that most other Americans don’t: whether to enroll in Medicare while keeping the Federal Employees Health Benefits (FEHB) plan you’ve had for decades. It’s not a simple choice, and the wrong answer can cost tens of thousands of dollars over a retirement — either in unnecessary premiums or in gaps in coverage that show up at the worst possible time.
The mistake most federal retirees make is assuming it’s Medicare or FEHB. It’s usually both — but exactly how “both” works, and whether to enroll in Part B specifically, is where the real decision lives.
This guide walks through the actual mechanics: what Medicare offers a federal retiree, what FEHB does, how they coordinate, and how to think about the Part B premium question that hits at 65.
What FEHB gives you as a federal retiree
If you retired from federal service with at least five years of continuous FEHB enrollment, you can carry your FEHB plan into retirement for the rest of your life at the same premium share the government pays for active employees. That’s an extraordinary benefit that most private-sector retirees don’t get.
FEHB in retirement:
- Covers you (and eligible dependents) with the same plan choices offered to active federal employees
- Includes prescription drug coverage in most plans
- Has no age-based cutoff — you keep it whether you’re 65, 75, or 95
- Costs roughly $300 to $700 per month depending on the plan (government pays about 70%, you pay 30%)
For most federal retirees, FEHB is already good enough as standalone coverage. The Medicare decision is really about whether to add on to it, not whether to replace it.
What Medicare gives you at 65
Medicare has four parts, each with different rules for federal retirees.
Part A — Hospital insurance. Free if you or your spouse paid Medicare taxes for at least 40 quarters (10 years) — which virtually every federal employee has done since 1983. Every federal retiree should enroll in Part A at 65. It’s free, it covers hospital stays, and it acts as a secondary insurance behind FEHB. There’s no downside.
Part B — Medical insurance. The one you decide about. Part B costs $185/month in 2026 for most retirees (higher for high-income enrollees due to IRMAA). It covers doctor visits, outpatient care, medical equipment, and preventive services. This is where the real decision is.
Part C — Medicare Advantage. Optional private-plan replacement for Parts A and B. Most federal retirees skip this, since FEHB already provides broader coverage.
Part D — Prescription drug coverage. Optional if your FEHB plan already includes drug coverage — which most FEHB plans do. Most federal retirees skip Part D.
How FEHB and Medicare coordinate
The mechanics of how these plans work together is what makes the decision non-obvious. Here’s what actually happens.
If you have both FEHB and Medicare Parts A and B:
- Medicare becomes primary — it pays first
- FEHB becomes secondary — it pays after Medicare, covering most or all of what Medicare didn’t
- Most FEHB plans waive your deductibles and copayments when Medicare is primary — you effectively have first-dollar coverage
- You pay two premiums: FEHB (~$300-700/month) and Medicare Part B ($185/month standard)
If you have FEHB only (no Part B):
- FEHB is your primary and only coverage
- You pay your FEHB deductibles and copays as usual
- One premium — just FEHB
If you have Medicare only (dropped FEHB):
- Medicare is your only coverage
- You have no protection for what Medicare doesn’t cover
- Prescription drug coverage requires a Part D plan on top
- You can’t get FEHB back once you drop it — this is a permanent decision
The Part B question: worth the $185/month?
For most federal retirees, this is the whole decision. Adding Part B costs about $2,220/year in premiums ($185 × 12). Is that worth it?
Case for enrolling in Part B:
Deductibles and copays vanish. Most FEHB plans have deductibles of $350 to $500 per person, plus copays for specialist visits, ER visits, and hospital stays. With Part B primary and FEHB secondary, most of these disappear. If you’re seeing multiple specialists, having a chronic condition, or expecting significant medical use, the elimination of cost-sharing can easily exceed $2,220/year.
Broader provider network. Medicare accepts virtually every doctor and hospital in the country. Some FEHB plans have network restrictions — if you travel, spend winters somewhere warm, or want maximum flexibility on where you get care, Medicare’s universal acceptance matters.
Lower total out-of-pocket in a bad year. If you or your spouse has a serious illness — cancer, heart surgery, extended hospitalization — the combination of Medicare + FEHB typically means much lower out-of-pocket cost than FEHB alone.
Protection against future FEHB changes. FEHB plan terms change every year during Open Season. Retirees who have both Part B and FEHB have a hedge — if their FEHB plan gets worse, Medicare still provides a floor.
Case against enrolling in Part B:
You pay two premiums. Some retirees, especially those in good health with predictable, low medical use, calculate that they’re better off keeping FEHB standalone and pocketing the $2,220/year.
IRMAA at higher incomes. If your income puts you in an IRMAA bracket (Income-Related Monthly Adjustment Amount), Part B premiums can be $260/month, $370/month, or higher — up to $600+/month at the top bracket. The math changes at higher incomes.
Late enrollment isn’t cheap either. If you decline Part B at 65 and enroll later, you pay a lifetime late-enrollment penalty of 10% for each 12-month period you delayed. Federal retirees generally don’t qualify for the “still working” exception that private-sector workers use to defer Part B.
The 8-month Special Enrollment Period trap
Here’s the detail that surprises retirees: the 8-month Special Enrollment Period (SEP) that lets you enroll in Medicare Part B without penalty after your active employment ends does NOT apply once you retire.
The 8-month SEP is designed for people who had employer coverage while actively working past 65 — like a private-sector employee who stayed on their company plan past 65 and retired later. It does not extend to people who retire before 65 and delay Part B enrollment.
For federal retirees, the practical rule is:
- Enroll in Part B during your Initial Enrollment Period (three months before to three months after your 65th birthday), OR
- Enroll during the General Enrollment Period (January 1 to March 31 each year), with coverage starting July 1 and a lifetime late penalty applied
The window most retirees care about is the 7 months around their 65th birthday. That’s when the decision should be made carefully.
What most federal retirees actually do
Data from OPM and various federal retiree surveys puts the numbers roughly like this:
- Around 70% of federal retirees enroll in both FEHB and Medicare Part B
- Around 25% keep FEHB only, skipping Part B
- A small percentage drop FEHB (usually a mistake, and often regretted)
The 70% who take both are, on average, right for their situation — the combination of Part B + FEHB gives near-comprehensive coverage with minimal out-of-pocket. But that doesn’t mean it’s right for everyone. Retirees in excellent health with a low-cost FEHB plan and modest income can make a strong case for FEHB-only.
The spouse coordination piece
If you’re married and both spouses were federal employees, you’re each making this decision independently. Common patterns:
- Both spouses have FEHB and Part B — highest cost, lowest medical risk
- One spouse enrolled through family FEHB, only that spouse takes Part B
- Both spouses drop Part B and rely on FEHB Self Plus One coverage
The right pattern depends on income, health, and whether either spouse has significant medical use.
When to actually decide
Not at 65. Before 65 — ideally 6-12 months out.
Signal the decision by:
- Getting an actual quote of your FEHB plan’s deductibles and copays for the year you’ll be 65
- Modeling your annual medical use (or your spouse’s) — how many specialist visits, prescriptions, procedures
- Confirming your income for IRMAA impact on Part B premium
- Understanding whether you’ll want the flexibility of nationwide Medicare acceptance (relevant if you snowbird or travel a lot)
The math almost always favors enrolling in Part B for retirees over a certain medical-use threshold, and it almost always doesn’t for retirees below it. Working out where you fall is a two-hour exercise that will affect your retirement cash flow for decades.
What we tell federal retirees at Stonebridge
The FEHB + Medicare coordination decision at 65 is one of the four core decisions we cover in every Federal Retirement Report — alongside pension election timing, Social Security claiming, and TSP withdrawal strategy. It doesn’t stand alone. Your income after retiring, your TSP withdrawal timing, and your Social Security decision all interact with Part B premiums through IRMAA and through your general cash flow.
If you’d like a personalized walkthrough of the decision for your situation — including how IRMAA looks for your projected retirement income and whether your specific FEHB plan makes Part B enrollment more or less compelling — you can request a free Federal Retirement Report that covers this along with the other core retirement decisions. There’s no charge and no obligation.
At the very least: enroll in Part A at 65 (it’s free), and decide about Part B before the window closes. Waiting is one of the few Medicare decisions that has a permanent penalty attached.