It is a short form of “bet you“: meaning that you are very sure about something.
It represents the sound of the phrase bet you when it is spoken quickly or it is used especially in the phrase you betcha as an enthusiastic way of saying “yes”
- I betcha some of them even considered leaving the team.
- A: “Hey Frank, do you want to come with us to the movies?” B: “You betcha I do!”
I betcha is colloquial for I bet you and You betcha is colloquial for You bet. In AmE.
I bet you and You bet.
- I bet you (I betcha) can finish on time.
- Do you think you can finish on time? You bet (You betcha).
Often, “you bet” is seen like this: You bet I can.
And the meaning, as an answer, means: Of course, I can.