Glossary
Medicare Part B
The medical insurance side of Original Medicare — covers doctor visits, outpatient care, preventive services, and durable medical equipment.
Also known as: Medical Insurance, Part B, SMI, Supplementary Medical Insurance
What is it?
Medicare Part B is the medical insurance component of Original Medicare. It covers physician services, outpatient hospital care, preventive screenings, lab work, durable medical equipment (DME), ambulance transport, and many other outpatient services. Unlike Part A, Part B has a monthly premium for everyone.
Why does it matter?
Part B is the single most important piece of the Medicare puzzle for retired military. **Without Part B, you lose TRICARE For Life.** The Defense Health Agency requires both Parts A and B to remain enrolled to keep TFL active at any age you're eligible for Medicare.
When you'll encounter it
You enroll during your Initial Enrollment Period (3 months before, the month of, and 3 months after your 65th birthday). If you're already on Social Security, Part B starts automatically but you may decline it — do not decline if you want to keep TFL.
Impact on Medicare
Part B pays 80% of the Medicare-approved amount for most covered services after you meet the annual Part B deductible. You're responsible for 20% coinsurance and the deductible.
Impact on TRICARE For Life
TFL becomes your secondary payer for Part B services. For services covered by both Medicare and TRICARE at a Medicare-participating provider, TFL typically pays the 20% coinsurance and deductible — leaving you with $0 out-of-pocket.
Impact on Medicare Advantage
A Medicare Advantage plan replaces how Original Medicare delivers Part B benefits — you still pay the Part B premium to Medicare, but the plan administers your care. Many veteran-focused MA plans include a 'Part B giveback' that reduces what's deducted from your Social Security check.
Common misconceptions
- "TRICARE counts as creditable coverage so I can skip Part B without a penalty." — Wrong. TRICARE does not qualify as employer group coverage for a Special Enrollment Period. Skipping Part B triggers permanent late penalties AND terminates your TFL.
- "Part B is optional once I'm retired." — It is technically optional, but declining it ends your TRICARE For Life coverage.
Related glossary terms
Last reviewed January 2026 against the 2026 Medicare & You and TRICARE For Life handbooks.