Lose your marbles
/luːz jɔː ˈmɑːblz/informalUK · US
What does “Lose your marbles” mean?
Lose your marbles means to stop thinking sensibly or clearly
You might joke that you have lost your marbles after putting your keys in the fridge. It can also express disbelief at an impractical plan.
It is not a medical description. Avoid it when someone is worried about their memory or mental health.
When do people say it?
Often used jokingly about your own forgetfulness or a wild idea. Saying it about someone else can be insulting, especially about memory problems.
“I put my keys in the fridge. I must be losing my marbles.”
Is it formal or informal?
Register: informal. It is most at home in everyday conversation rather than formal writing. Most common in UK and US.
Where does it come from?
“Marbles” is an informal word for a person’s wits or good sense. Losing them means no longer thinking clearly; it is not about a game here.
Origin confidence: Disputed; treat with caution
How do you say “Lose your marbles” in other languages?
Related idioms
- Not playing with a full deck, not thinking sensibly or clearly, said as an insult
Last updated 2026-10-01