You can see when your course access expires on your account's course list page. The expiration date for each of your courses is always shown on the top left of the course card here, so that you can keep track of when your access expires:

The expiration date shown on the class card is the date that the access to the course that you purchased ends. You should plan to finish your course before this date. After this date you will lose access to the course.

If you need to download your education certificate after your access expires, don't worry: Your course completion certificate will still be available on the "Your Completion Certificates" page of your account.