We don't keep track of that unless you mean display their expiration date. You can display their expiration date using the below substitution anywhere Joomla content plugins are supported.
[cbsubs:subscriptions plan="PLAN_ID" output="expiry_date" /]
Check the description of the cbpaidsubsbot system plugin within Extensions > Plugins for further CBSubs substitution usage information.
Aside from that you can try using the CBSubs module included with CBSubs, which displays some information regarding their subscription.