Your current subscriptions and premium membership expiration date can be checked at any time  in your profile by clicking on Account Settings

If your membership subscription is recurring, you will see the renewal date rather than an expiration date. You can cancel the recurring payments at any time (and at least 24 hours before the expiry date preferably) and your membership will continue until the expiry date shown in the subscriptions section of your dashboard, cancelling the payments only stops the membership from renewing automatically in the future, it will not affect any payments that have already been processed.