Let the cat out of the bag is a picture of a secret escaping. The bag is closed, the secret is hidden inside, and then someone opens it. After that, there is no putting the cat back.
The idiom usually suggests an accident. The person did not plan to tell, but a word, a look or a badly chosen sentence gave the game away.
This page explains the meaning, the grammar, the register and the alternatives such as spill the beans. The 10-question drill at the end explains every answer.
What it means
In one sentence: To let the cat out of the bag means to reveal a secret, usually by mistake and often before the right moment.
What the idiom means in everyday English
- It means a secret has become known: "Who let the cat out of the bag?"
- It usually implies an accident, unlike a deliberate announcement.
- It fits surprises, plans and private news between friends or colleagues.
- The image is final: once the cat is out, the secret cannot be hidden again.
How the idiom behaves in a sentence
- The fixed pattern is let the cat out of the bag: "Do not let the cat out of the bag."
- The verb changes with tense: let, lets, letting. The past form is also let, not letted.
- Common patterns are let the cat out of the bag about something and the cat is out of the bag.
- The articles stay fixed: the cat and the bag, never a cat or a bag.
When the idiom does not fit
- Do not use it for a planned announcement. It is for secrets that escape.
- It is too light for serious leaks or confidential business information.
- Avoid it in formal writing; say "the information became public".
- Do not use the singular bag with a plural cat: the fixed phrase is one cat and one bag.
Use it or not
Register: Informal. Let the cat out of the bag fits conversation, messages and friendly writing. It is common in British and American English, with British English using it a little more. In formal writing, use "revealed the information" or "the secret became known". The phrase is playful and never rude.
Examples
- I let the cat out of the bag about the party by accident.The accident is stated clearly.
- Who let the cat out of the bag about the new office?A question about the source of the leak.
- The cat is out of the bag now; everyone knows about the merger.The present form describes a secret that is already public.
- He did not mean to let the cat out of the bag, but he mentioned the surprise.The idiom often follows did not mean to.
- We cannot hide it any more; the cat is out of the bag.The idiom shows the secret cannot be returned.
- She let the cat out of the bag when she asked about the cake.One careless question can reveal the secret.
- Try not to let the cat out of the bag before Friday.The negative instruction keeps the surprise safe.
Similar idioms
spill the beans
to reveal a secret, often before the right time.
let slip
to say something without meaning to.
give the game away
to reveal a plan or a trick by accident.
blurt out
to say something suddenly, without thinking.
the secret is out
the plain phrase for a secret that has become known.
Practice drill
Answer all 10 questions. Each answer is marked at once, and the meaning is explained under the question.
We wanted to keep the news quiet, but Tom ___ at dinner.
Show answer and explanation
Answer: A. let the cat out of the bag Let the cat out of the bag means to reveal a secret, which is what Tom did with the news.
Which sentence uses let the cat out of the bag correctly?
Show answer and explanation
Answer: B. She let the cat out of the bag about the surprise trip. The idiom means revealing a secret; the other sentences use the words literally or describe the opposite action.
What does let the cat out of the bag mean?
Show answer and explanation
Answer: C. to reveal a secret Let the cat out of the bag is an idiom for revealing a secret, usually by mistake.
The engagement was supposed to be a surprise, but Maya mentioned it. What did she do?
Show answer and explanation
Answer: D. All three are correct. Let the cat out of the bag, spill the beans and give the game away all mean revealing a secret or a plan.
Which situation fits the idiom best?
Show answer and explanation
Answer: A. a friend accidentally mentions a surprise party The idiom is about a secret escaping by accident, and the surprise party is exactly that; announcements and recipes are not secrets.
Choose the sentence with the same meaning: "He let the cat out of the bag."
Show answer and explanation
Answer: B. He revealed the secret. Let the cat out of the bag means to reveal a secret, so the sentence is a plain version of the same idea.
Which is correct?
Show answer and explanation
Answer: C. The cat is out of the bag now. The fixed phrase keeps one cat and the article the: the cat is out of the bag.
Your colleague says, "We cannot hide the plan any more." What can you reply with?
Show answer and explanation
Answer: D. You are right; the cat is out of the bag. The cat is out of the bag means the secret is already known, which matches the colleague’s point.
Which sentence does NOT use the idiom correctly?
Show answer and explanation
Answer: A. The cat let the bag out of the house. The last sentence reverses the phrase and uses the words literally; the idiom means to reveal a secret.
A friend asks how the surprise was ruined. What is a natural answer?
Show answer and explanation
Answer: B. I let the cat out of the bag by accident. Let the cat out of the bag means to reveal the secret, so it answers how the surprise was ruined.
Questions learners ask
Is let the cat out of the bag formal or informal?
It is informal. Use it in conversation, messages and light writing. In a formal report, write "the information became public" or "the plan was disclosed".
What is the past tense of let the cat out of the bag?
The past tense of let is let: "He let the cat out of the bag." English does not use letted. The time phrase shows the tense.
Why does the idiom talk about a cat and a bag?
The phrase is recorded in English from the 1700s. One old story says dishonest traders sold a cat instead of a pig in a sack, but that story is not documented, so the real reason for the cat and the bag is unknown.
More idioms
Kick the bucket
To kick the bucket is a very informal way to say that someone has died.
See eye to eye
To see eye to eye with someone is to agree with them or share the same opinion.
Pull someone’s leg
To pull someone’s leg is to joke with them by saying something that is not true, in a friendly way.
Browse all the idiom pages or take the free A1 to C2 level test to find your starting point.