While not foolproof, this will usually get you the answer. Go to www.flightstats.com . Look at today and hope that the schedule will be the same when you fly. Find your flight and see what gate it is leaving from. Then look at all flights arriving at your airport and find which flight is coming to the gate your flight is leaving from. If that flight has the same flight number, then it is a through flight. If that flight is a different flight number, then everybody will be getting off and yours will be an originating.