Short answer: TRICARE For Life is wraparound coverage for TRICARE-eligible people who have Medicare Part A and Part B. It is automatic once both are in effect, but the beneficiary must pay the Part B premium.
TRICARE For Life (TFL) is Medicare-wraparound coverage for people who are TRICARE-eligible and have Medicare Part A and Part B, regardless of age. There is no separate enrollment or enrollment fee; coverage starts the first day Part A and Part B are in effect, and the Medicare card plus the uniformed services ID card serve as proof.
How claims work: Medicare pays first, then the TFL claims processor pays the rest for services both cover. Generally the beneficiary has no out-of-pocket cost for services covered by both Medicare and TRICARE. For services only TRICARE covers, the TRICARE deductible and cost-shares apply. Overseas, TRICARE pays first, and Part B is still required to keep TRICARE.
Because TFL fills most of Medicare’s cost-sharing, a Medicare supplement is often redundant for people who have it; check the situation before buying one. Each person needs their own Part A and Part B to have TFL.