I want to return my car early; is there a penalty to do so?

At Enterprise you will only be charged for the days you had the vehicle (excluding prepaid reservations). 

There is no penalty fee for returning the car early. You will only be charged for the days you had the vehicle. The system will amend the rate to reflect the new length of car hire as of the time you made your booking. this may change the daily rate applied over the length of your hire.