〜だろう: probably (plain)

Plain form of でしょう: shows a guess about something.

Plain form + だろう. Used by men in speech or in writing and news. 〜だろうか is a question to yourself, and 〜だろう？ with rising tone seeks agreement. 〜でしょう is the polite version. Women usually use 〜でしょ in casual speech.