(it) beats me

(it) beats me

slang A response when one does not know the answer to a question. A: "How long has this milk been in the fridge?" B: "Beats me. Check the expiration date." When's Ali's birthday? Beats me! It beats me—I have no idea how to get to the mall from here.
See also: beat
Farlex Dictionary of Idioms.

(It) beats me.

 and (It's) got me beat.; You got me beat.
Inf. I do not know the answer.; I cannot figure it out. The question has me stumped. (The stress is on me.) Bill: When are we supposed to go over to Tom's? Bill: Beats me. Sally: What's the largest river in the world? Bob: You got me beat.
See also: beat
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

beats me

This baffles or puzzles me, as in I don't know how he does it-beats me! This term originally may have alluded to a winning poker hand. It may also be related to the even earlier usage of beat for "astonished" or "at a loss." [Slang; mid-1800s]
See also: beat
The American Heritage® Dictionary of Idioms by Christine Ammer.

it ˌbeats ˈme (why, how, etc.)

(informal) I cannot understand (why, how, etc.): It beats me how he can afford a new car on his salary. What she does with her time beats me.
See also: beat
Farlex Partner Idioms Dictionary

beats me

tv. [the answer is] not known to me. (The emphasis is on me.) I don’t know the answer. Beats me!
See also: beat
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • beats me
  • it beats me
  • search me
  • search me!
  • you got me beat
  • (you/it's) got me beat
  • check through
  • have passed (someone's or something's) sell-by date
  • have passed your sell-by date
  • play a practical joke (on one)