bank asks where my company's start-up capital comes from

Origin of funds, not of every deposit

Yes, this is a question the bank must ask, and it usually concerns the origin of the company's funds in a broader sense — not a bookkeeping breakdown of every euro of starting capital. The bank asks this as part of its customer due diligence and wants to understand whether the money is logically explainable: the founder's own contribution, a loan, an investment, or acquired activities. A brief, factual answer is usually sufficient — an extensive reconstruction of the first annual accounts typically is not.

Supporting documents often requested for this: an extract or founding deed from the business register, a bank statement of the deposit, or a loan agreement if the capital was borrowed. If you no longer have that at hand, then "no, not available" is a more honest answer than guessing — this field belongs in the source of the company's assets, and that question often appears in the same section as the question about the ultimate beneficial owners of the company. Banks often combine both, because origin of funds and UBO structure are reviewed together in their own risk assessment.

Where this follows from the Wwft

The obligation does not come from the bank itself, but from the Law on the prevention of money laundering and the financing of terrorism. That law requires banks to conduct customer due diligence, and investigation into the source of funds is part of that as part of the customer's risk profile. How thoroughly that investigation goes depends on the risk the bank assigns to the customer — a sole proprietorship with modest starting capital typically receives fewer follow-up questions than a structure with foreign cash flows or complex ownership arrangements.