The previous answer (relating to 2013, same as 2016) is not really the answer.
In previous versions, I was able to have the Outlook calendar automatically assign color categories to events (travel, client meetings, etc.). In Outlook 2013, I can't figure out how to accomplish this seemingly simple task. I just want my events to be color coded based on key words entered in the description. For example, if "travel" is in the description, then the event is color coded red.
Have you tried creating conditional formatting rules? Right-click on the calendar, select View Settings, then select Conditional Formatting. Create your rules.
Wow, that was easy, but it doesn't put the item into a category, it just formats the color. If Outlook is going to the trouble of having the front end of a filter (the IF) then why not have the back end of the filter (THEN) and allow the item to be assigned to an actual category not just a useless color? I have appointments that still automatically categorize because I set it up in 2007 or before but I cannot access that capability anymore for new categories. Frustrating because it still exists, just not accessible unless there is another way than the one suggested above. Help!