What they are really asking
This is a close cousin of the outside income question, and it's just as personal. Your savings, your investments and what you earn from a hobby are private in most situations. In many countries interviewers shouldn't ask about them at all, except where the job has a real reason.
That real reason is usually a conflict of interest. If you'll be buying supplies for a company, managing its money or working with clients' investments, the employer may need to know whether you own shares in a supplier or run a side business in the same field. Many of these companies have a formal form for this. For most other jobs, the question is really about time: does your hobby business take energy away from the work?
A shape that works
Separate the hobby from the business, and the private from the relevant. If you earn a little from a hobby, say so in a sentence and make clear it's small and separate. If you have ordinary savings or a retirement fund, you can say that without any details. If the role involves money or purchasing, offer to complete any declaration they need. Friendly, brief, then back to the job.
Model answers
Listen to how each answer is built, then make it yours.
Check yourself
Practice · 3 min
Record a thirty-second answer that follows the shape: say whether you earn anything from a hobby or investments, keep any details private, and confirm there's no clash of time or interest. If the job involves money, offer to complete a declaration. Listen back and check that you used the idea of "separate" somewhere.
Your recording stays on this device. Nothing is uploaded.
Say it today
Use it once in a real conversation before tomorrow. Out loud counts, even to yourself.