Count in Definition 1 of 3Pro Tip 1/3Active Participation Used when enthusiastically joining an activity or group. They're playing soccer on Saturday? Count me in! Pro Tip 2/3Confusing with 'count on' 'Count in' means to include, while 'count on' means to rely on someone. I'll count you in for dinner, but I'm counting on you to bring dessert. Pro Tip 3/3Voluntary Inclusion Implies a positive response to an invitation without being forced. There's a team project? Great, count me in!