No. If you don't use all the classes from one month, we will roll them over to the following month. This is especially helpful if you are going on vacation, or you need to cancel a class last minute (remember: at least 2h before the scheduled time).
Your classes will accumulate, and you will never lose them, as long as your subscription is still active.
Please note: if you cancel your subscription, you will not be able to enjoy your accumulated classes.