Do I need business registration for a side hustle or a few online sales in Hong Kong?

Hong Kong law does not set a minimum turnover below which a business need not register. The question is whether you are carrying on a business, which is decided on the facts.

Factors that point towards a business include repeated purchases of goods for resale, a profit motive, an organised set-up such as a shop page or regular listings, holding stock, and spending on advertising. Occasionally selling second-hand items you owned for personal use points the other way.

The tests used by the IRD for profits tax follow the same logic: a trade or business, as opposed to an isolated or private transaction. Being part-time or doing it alongside a job does not stop it being a business.

The official pages do not give a simple threshold, so if you sell regularly for profit, treat yourself as running a business and register. If you are unsure, the Business Registration Office can be asked directly. Registering does not by itself create a tax bill; profits tax is charged only on assessable profits.