The most important thing to know about Medicare Supplement Insurance is that timing is everything. If you don’t sign up for a Medicare Supplement policy within six months of when your benefits kick in under Original Medicare, insurers can charge you substantially more or deny coverage altogether if you have a preexisting condition. This critical window ensures you can get the coverage you need at an affordable price. Medicare Supplement insurance is a private policy that helps lower your out-of-pocket health costs and works only with Original Medicare (Parts A and B). While Original Medicare covers many services, it has deductibles and coinsurance without an annual or lifetime limit on out-of-pocket costs. About one in four people with traditional Medicare get a Supplement plan, and during your six-month open enrollment, insurers must sell you a policy regardless of health. Exceptions to this rule exist in Connecticut, Massachusetts, Maine, or New York, or if you switch from Medicare Advantage within 12 months, or if your Advantage plan withdraws from your area. Another option is a Medicare Advantage plan, which covers hospitals, doctor visits, and often prescription drugs, but typically has more restrictions and higher out-of-pocket costs than Original Medicare plus a Supplement plan.