Who Is Eligible For Medigap Coverage? 
You are eligible for Medigap coverage if you have both Medicare Part A & Medicare Part B active . When you first enroll in Part B , you trigger a 6-month initial open enrollment period to buy a Medigap plan -LRB- also known as Medicare Supplement plans -RRB- with NO MEDICAL UNDERWRITING . This is the BEST time to buy a supplement plan because regardless of your medical history , you can buy any Medigap plan from any carrier and can not be declined . Plans F and G offer the most comprehensive coverage and therefore the most predictable expense structure - a major benefit for individuals on a fixed income . Please note , Medigap plans are standardized so the difference between carriers is price - plan F is the exact same plan F from every insurance company . Beyond this window , you 'll be subject to answering health questions to qualify for a new plan -LRB- every carriers ' questions are different -RRB- if you do n't have a guaranteed-issue right available to you . If you 're under 65 , you can still purchase a Medigap plan if you 're on Medicare for disability or ESRD , but the cost will be very high . Medigap plans are designed to be purchased by individuals age 65 and up . Under age 65 individuals on Medicare will likely either buy a Medicare Advantage plan or stay under original Medicare -LRB- Parts A & B -RRB- and add a stand-alone Part D plan for their prescription drug coverage . I hope the information is helpful - please feel free to contact me for help with your coverage and if you have any other questions . Thanks very much . 