Medigap Plans: also called Supplement Plans are provided by private insurance companies. Medigap plans only work with "Original Medicare" and can cover much of the 20% cost sharing you would have to pay with "Original Medicare". There are presently eleven plans (A,B,C,D,F, select, G,K,L,M and N). Plan A is the basic plan and as you go up the alphabet each plan provides more benefits and increased premiums. Note: all plans are identical for all carriers except for the premium. Medigap or Supplement Plans offer great coverage, however, you can enroll and receive guaranteed acceptance for only six months after you have started your Part B. Later you would be able to enroll in a Medigap Plan, but with underwriting your premium could be rated higher or you could be declined.