From Longman Dictionary of Contemporary EnglishI bet/I’ll betI bet/I’ll betspoken a) SUREused to say that you are fairly sure that something is true, something is happening etc, although you cannot prove this Bet 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 pink dimples bobbing up and down there.• Yes, there was something in there and I bet myself it would be Jo's emerald pendant.• 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 slightest intention 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. 