give us some more information on your trips and where/how you drive. There can be multiple reasons for this. First reason that comes in mind is are you driving very short 5-10 miles trips? Are you driving on a freeway or internal roads? what speeds? Battery pack health?
Post #1 in this thread Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat contains a questionnaire that could greatly help everyone here diagnose your problem. Please post your answers to most of them on this thread and give us a chance to give you accurate help instead of just blindly guessing.
Did this just start recently? You were doing better before? Any recent maintenance, tire changes, brake work? As previously mentioned: change in driving conditions?
