From Longman Dictionary of Contemporary EnglishI bet/I’ll betI bet/I’ll betspokena)SUREused to say that you are fairly sure that something is true, something is happening etc, although you cannot prove thisBet you wish you’d arrived earlier.I bet you she won’t come.b)UNDERSTANDused to show that you understand or can imagine the situation that someone has just told you about‘God, I was so angry.’ ‘I bet you were.’‘It makes things much easier.’ ‘Yeah, I’ll bet it does.’c)BELIEVE#used to show that you do not believe what someone has just told you‘I’m definitely going to give up smoking this time.’ ‘Yeah, I bet!’ →bet
Examples from the Corpus
I bet/I’ll bet• He'll be really pleased to see you, I bet!• Ever since he got ill - for nearly a week, I bet.• My dentist would laugh at me, I bet.• Jealous of her. I bet it really got him going seeing my little pinkdimplesbobbing up and down there.• Yes, there was something in there and I bet myself it would be Jo's emeraldpendant.• I bet she hasn't told her parents about this.• I bet that the meeting will be cancelled again.• Why, I bet you never had the slightestintention of following through last night, did you?• Come and sit down, I bet you're exhausted.• I bet you're tired after such a long journey.• P.S. I bet you won't print this.