Medigap is health insurance that supplements the benefits covered under Medicare. It also fills in some of the gaps left by Medicare, such as your deductible and coinsurance contributions. Sold by private insurance companies, Medigap insurance is offered in 12 different versions, Plans A through L (except in Massachusetts, Minnesota, and Wisconsin, which have their own standardized plans). Each provides a different level of coverage, but not all plans are available in all states.

Plan A covers the following basic benefits:

• Your coinsurance contribution for hospital visits that Medicare covers
• Full coverage for 365 additional hospital days for use after Medicare's coverage of 60 days is used up
• Your coinsurance contribution on doctors' bills that Medicare covers
• The first three pints of blood you may need in a year (Medicare pays for any additional blood)

Plans B through J cover the same basic benefits, plus some extra benefits that include different combinations of the following:

• The hospital deductible for visits that Medicare covers
• Daily coinsurance contribution for skilled nursing facility care
• The deductible for doctors' services that Medicare covers
• Eighty percent of emergency medical costs that are needed during the first two months of a trip outside the United States
• The difference between your doctor's fee and Medicare's allowance
• Custodial care, working together with Medicare's coverage
• Routine annual medical checkups and other preventive care

Plans K and L have lower premium costs than other Medigap plans, but require you to pay some higher coinsurance costs. However, they provide protection against catastrophic illnesses by limiting your annual out-of-pocket expenses. These plans include the following benefits:

• 50 percent (Plan K) or 75 percent (Plan L) coverage of the skilled nursing facility, hospice, and respite care coinsurance costs and the hospital deductible under Medicare Part A
• 100 percent coverage of hospital inpatient coinsurance costs and 365 additional lifetime days of coverage for inpatient hospital services
• 100 percent coverage of the Medicare Part B coinsurance costs for preventative benefits
• 100 percent coverage of all coinsurance costs for the rest of the year once an annual out-of-pocket limit is met

Some of the benefits not covered by Medigap include long-term nursing home care, and vision and dental care. Medigap will follow Medicare in excluding what is unnecessary or experimental.

If you are covered by your former employer's health insurance plan, you may not need Medigap.