Start with who pays first
Payer order changes how much coordination value Part B can provide. OPM states that FEHB is primary for an active federal employee or a reemployed annuitant eligible for FEHB when the enrollee or covered spouse also has Medicare. OPM states that Medicare is primary for an annuitant, with exceptions including eligible reemployment and special rules for disability, end-stage renal disease, and workers' compensation.
The primary payer processes the claim first. The secondary payer may cover some or all of the remaining eligible amount, but it does not promise that every balance is paid. Tell the FEHB carrier about Medicare coverage so claims can coordinate correctly, and use the plan brochure's Medicare section for the actual rules.
| Situation | Generally primary | Generally secondary |
|---|---|---|
| Active federal employee with FEHB and Medicare | FEHB | Medicare |
| FEHB annuitant with Medicare | Medicare | FEHB |
| Reemployed annuitant eligible for FEHB | FEHB | Medicare |
Price the second premium against plan-specific savings
Part B has its own monthly premium, and income-related adjustments can increase it. OPM says adding Medicare does not reduce or increase the FEHB premium; the FEHB deduction continues unless the enrollee changes plans, options, or enrollment status through a permitted election.
For annuitants, some FEHB options waive deductibles, copays, or coinsurance when Medicare is primary. Some options may reimburse part of the Part B premium or offer a Medicare Advantage arrangement accessed through the FEHB plan. Those features differ by option and can change, so calculate annual Part B premiums and compare them with documented plan savings and provider access.
- Estimate the household's annual Part B premiums, including any income-related adjustment.
- Read the plan's Medicare coordination section for waivers, reimbursement, and network rules.
- Check prescriptions and Part D coordination separately from Part B medical coverage.
- Compare the same FEHB enrollment tier and plan status before drawing a cost conclusion.
Do not miss the HSA and enrollment consequences
Medicare enrollment and HSA contributions cannot be treated independently. OPM says an enrollee is not eligible to make HSA contributions while enrolled in Medicare and warns about Medicare Part A retroactivity. The current OPM guidance says to stop HSA contributions at least six months before enrolling in Part A or Part B; confirm the exact timing for your facts before applying.
Becoming eligible for Medicare is also a qualifying life event that can create a one-time FEHB plan-change opportunity. For annuitants, suspension and cancellation are not synonyms: OPM warns that cancellation is generally permanent, while qualifying suspension for a Medicare Advantage plan can preserve a path to reenroll. Obtain retirement-system instructions before acting.
Questions about this FEHB decision
Does Medicare Part B replace FEHB?
No. Many enrollees keep both and coordinate benefits. Payer order and the value of the combination depend on active or annuitant status and the specific FEHB option.
Will my FEHB premium go down after I enroll in Part B?
No automatic reduction applies. OPM says the FEHB premium stays the same unless you change plans or options; some individual plan options may separately reimburse part of the Part B premium.
Which pays first, FEHB or Medicare?
FEHB generally pays first for an active federal employee, while Medicare generally pays first for an annuitant. Reemployment, disability, ESRD, workers' compensation, and other facts can change the order.
Can I contribute to an HSA after enrolling in Medicare?
No. Medicare enrollment makes a person ineligible to make or receive HSA contributions. Review Part A retroactivity and stop-contribution timing before enrollment.
Primary sources
Reviewed August 25, 2026. Each source below is an official federal page used for the claims on this resource.
- OPM Medicare and FEHB overview (opens in a new tab)
Current FEHB coordination, premium, HSA, and enrollment-choice guidance.
- OPM guidance for active federal employees (opens in a new tab)
Part B considerations, special enrollment, and FEHB-first guidance while actively employed.
- OPM guidance for annuitants (opens in a new tab)
Cost-sharing, Part B, late-enrollment, and annuitant coordination considerations.
- OPM payer-order guide (opens in a new tab)
Common primary-payer situations and important exceptions.
- CMS Medicare Secondary Payer overview (opens in a new tab)
Federal coordination-of-benefits framework for Medicare and employer coverage.
This is general educational information, not legal, tax, financial, medical, or enrollment advice. OPM, your employing office or retirement system, the carrier brochure, Medicare, and the plan administrator control your actual eligibility, timing, costs, and coverage.