Be aware that under federal law, Medigap policy insurers can refuse to cover your prior medical conditions for the first six months. A prior or pre-existing condition is a condition or illness you were diagnosed with or were treated for before new health care coverage began.

The wait time for your Medigap coverage to start is called a pre-existing condition waiting period. You can avoid such waiting periods if you buy your policy when you have a guaranteed issue right. If you buy your policy when you have a guaranteed issue right, the insurer cannot impose a waiting period for coverage of any prior medical condition.

You can also avoid or shorten a pre-existing condition waiting period if you buy a policy during your open enrollment period. During this protected period, Medigap policies must shorten any pre-existing condition waiting period by the number of months you had prior creditable coverage. Most forms of health coverage count as creditable.

Here’s how this works: your pre-existing condition waiting period is reduced by one month for each month you were enrolled in creditable coverage prior to purchasing a Medigap. If you had creditable coverage for two months before you purchased a Medigap, your policy could only impose a four month waiting period, instead of six months. If you had six or more months of prior creditable coverage, Medigap insurers must cover your prior medical conditions immediately. Keep in mind that you cannot use creditable coverage to reduce your pre-existing waiting period if you had a break in coverage of more than 63 days.

Make sure to consider several Medigap policies, especially if you are concerned about facing a waiting period. Some policies do not impose pre-existing condition waiting periods.