A common misconception is that Medicare's Annual Election Period covers Medicare Supplement plans. The election period runs each year from October 15 through December 7, but it only applies to Part D and Medicare Advantage plans.
So when can you cancel a Medicare Supplement plan? You might want to cancel your current Medicare Supplement plan and replace it with a different Medigap plan. The good news is you can do this at anytime. That said, unless you find yourself in a guaranteed issue situation, you'll have to undergo health underwriting.
Unlike other types of insurance - disability insurance, for example - Medigap underwriting doesn't require a medical exam. The process is usually pretty quick and involves answering a few health questions on the application.
As Medicare Plan F is discontinued for new enrollees in 2020, rates are expected to increase for those remaining on Plan F. While you can cancel your Plan F anytime, switching to a new plan will likely require underwriting, so the best time to make the switch is while you're still in good health.