Why interviewers ask this question
"Tell me something not on your CV" (or variants: "Tell me something interesting about yourself," "What would your friends say about you that is not on your CV?") is asked to get below the polished professional surface you have curated on your application. The interviewer is looking for: genuine personality, interests that say something about how you think or what you care about, and authenticity. The question rewards candidates who have actual lives and interests outside work and who can talk about them with genuine engagement. It penalises candidates who either go completely blank or who give a thinly disguised work achievement dressed up as a personal fact.
What makes a good answer
A good answer to this question has three qualities: it is genuine (not something you researched as a good answer), it reveals something interesting about you as a person, and it gives the interviewer something to engage with or follow up on. Strong categories: an unusual skill or hobby ("I have been training in Brazilian jiu-jitsu for three years"), a non-work achievement that required discipline or creativity ("I ran my first marathon last year after ten years of being someone who genuinely hated running"), a learning project you are engaged with outside work ("I have been teaching myself Portuguese for the past two years — I use it on a trip to Brazil last year"), community involvement ("I coach an under-12 cricket team on weekends"), or something that reveals an unexpected interest ("I became obsessed with medieval history after visiting a castle with my kids and now I read about it regularly"). The specificity is what makes it compelling.
What to avoid
Do not give an answer that is really a work achievement ("I recently led a team project that..."). The interviewer specifically asked for something not on your CV. Do not give a generic answer that applies to everyone ("I love travelling" / "I enjoy spending time with family and friends"). These reveal nothing distinguishing. Do not give something calculated to seem impressive to a recruiter rather than something genuine ("I sit on three volunteer boards"). If it sounds like you researched what makes a good answer to this question, it will land that way. And do not give something that creates a risk (an extreme sport hobby that makes an employer worry about your health insurance), something politically loaded, or something genuinely private that you would rather not discuss once you have opened that door.
How to prepare
The best preparation: think about your actual life outside work and identify two or three things you are genuinely engaged with right now. Write down three sentences about each: what it is, how long you have been doing it, and one specific detail that shows genuine engagement rather than casual acquaintance. Practice saying them aloud so they come out naturally in the interview. Having two or three options gives you flexibility depending on the context — a creative agency interview and an investment bank interview might call for different selections from your list.