Domains are valid for 1 year from date of sign-up. You can choose for them to Renew automatically or not.
To cancel automatic renewal go to "My Domains" page via your Account's page and disable the auto-renewal.
Note that the custom domain info will only show to the admin that purchased the custom domain.
We suggest making a note on your calendar as canceling is your responsibility and domain charges are nonrefundable.
For domains purchased directly via support, your domains will not renew automatically.