Some worry that when they sign up for Medicare, they will pay more if they have pre-existing health conditions. That’s not true for Medicare or Medicare Advantage (MA) and Part D prescription plans. This also holds true for supplemental policies (Medigap) only if you sign up for it during your six-month Medigap open enrollment period. If you want it later, an insurance company can charge you more or refuse to sell you a policy because of your health status.
Source AARP Bulletin, June 2022.