bank asks how many transactions we expect per month, which number should I provide

Expected transaction volume is an estimate, not a dossier fact

There is no source document for this field that you can tick. The expected number of transactions per month is not a historical fact like a Chamber of Commerce number or a UBO percentage; it is an estimate that the customer must make themselves. The bank is not asking for this to check you, but to classify your account into a risk profile for customer due diligence: a company that receives money one hundred times per month from ten countries receives different monitoring than a company with five invoices from two regular customers.

A reasonable approach is to fall back on what is already known: the number of invoices or payments from recent months, possibly rounded to a round margin. If you do not have this history — for example with a newly started activity or a new account — then a substantiated estimate based on the expected order frequency is all you can provide. There is no "correct" figure with which you can automate this field from a fixed dossier; however, the answer can be revised over time if the actual volume clearly differs, as this is precisely what banks ask about periodically. This field is often linked to questions about at which banks the enterprise maintains accounts, because the volume sometimes differs per account or per bank.

Basis: customer due diligence, not business register

The bank's request for this follows from the Anti-Money Laundering and Counter-Terrorist Financing Act: customer due diligence requires the bank to understand the nature and purpose of the business relationship, and the expected transaction pattern is part of that. This is separate from the Trade Register Act 2007, which concerns only registered business data and contains no expectations about future behaviour — which is why you cannot obtain this field from a Chamber of Commerce extract. Compare this with the question about the average payment term to suppliers: that too is a business fact that the customer supplies themselves, not something that comes from an official register.