Medicare Part A covers hospital bills. Medicare Part B covers medical services like doctors’ services/visits, outpatient care, and other medical services that Part A doesn’t cover. If you have both, and your FEHBP, essentially between all your coverage, you will probably end up not paying having to pay any medical bills except for your prescription drugs. And if you don't sign up for Medicare Part B when you first become eligible, and later decide to sign up, there is a significant penalty (%) that you pay for that period between eligibility and sign-up. "The cost of Medicare Part B will go up 10% for each full 12-month period that you could have had Medicare Part B but didn’t take it, except in special cases. You will have to pay this penalty as long as you have Medicare Part B."
Check
view link click on "Am I Eligible" on the left side, then click on the upper tab "General Enrollment and Eligibility" for more info.
IMHO, to me it's worth it not having to worry about meeting FEHBP co-pays, deductibles, and max out-of-pocket each year. My take on this is that my Part B premium will be paid for by not having to meet the yearly deductibles and copays under FEHBP. We're not getting younger and our medical needs will increase.