You Bet

Also:
You bet your ass,
You bet your (sweet) life,
You can bet your bottom dollar,
You betcha

Meaning of Idiom ‘You Bet’

You bet means you can be absolutely certain; for sure; indeed; I completely agree. 1Heacock, Paul. Cambridge Dictionary of American Idioms]. Cambridge: Cambridge UP, 2010.,2Ammer, Christine. American Heritage Dictionary of Idioms. Boston: Houghton Mifflin Harcourt, 2013.

You bet is also used as an informal thank you response and as an affirmative response to a request.

Examples Of Use

“Are you coming to the party?” asked Frieda. “You bet!” replied Clark. “I wouldn’t miss it!”

“These people will do anything to stay in power,” said Paul. “You bet they will,” said Heath.

“Was that Brad Pitt eating in that restaurant?” “You bet it was!”

“Bill will be late again today. You can bet your ass on that.”

“Can you help me move this sofa?” “You bet. Just give me a minute.”

“Thanks for the help,” said Dan. “You bet,” replied Dex.

Origin

Used since the second half of the 1800s.

You bet is an allusion to gambling. This phrase and all its variations are used to mean that you can be so certain of something that you can bet something valuable on its being true, including your life or your bottom, or last, dollar.

As a thank you response, you bet seems to mean quite the same, that you can count on a person’s help.