ERcast offers 27 CME credits a year. Episodes are released on a weekly basis and you can claim CME at the end of each month by confirming that you have listened to the episodes. To listen and claim CME, log into your ERcast account and click on "CME". Once you have listened to at least one monthly episodes, you'll be able to print your CME Certificate.
ERcast listeners have the option to subscribe on a monthly or yearly basis. Your subscription will automatically be set to renew when you first subscribe, but you can turn that off anytime from the "Settings and Orders" tab of your ERcast homepage. As long as your subscription is active, you'll have full access to all of the ERcast episodes and CME. Once your subscription expires, you will no longer be able listen to any episodes, but you can renew anytime to regain access to all episodes and earn more CME.