what should I fill in for expected transaction volume per month

Expected transaction volume is an estimate, not a commitment

Expected transaction volume per month is the estimate of the amount that flows through the account: inflows and outflows, in euros or in number of transactions. The bank does not ask this out of curiosity about your turnover, but to establish a normal picture. The bank will later use this normal picture to signal deviations — a sudden increase or a pattern that does not match what you have stated will stand out. This is part of the customer due diligence that banks are required to conduct.

You can usually substantiate this with your latest annual figures or, if these are not yet available, with a turnover forecast. A range is more common than an exact figure — banks rarely ask for a figure to the nearest euro, but rather for an order of magnitude that matches your business size. If you have just landed a large new customer or are planning to expand internationally, that volume may well be higher than your historical turnover; it is the expectation that counts, not only the past. If you are in doubt between two ranges, choose the wider one: a volume that later turns out to be lower than stated gives fewer questions than a volume that exceeds the range. This question often appears in the same block as the source of the company's assets, because the bank assesses volume and source together to obtain a consistent picture.

Where this comes from: the customer due diligence of the Wwft

The obligation for banks to establish the expected transaction volume follows from customer due diligence under the Anti-Money Laundering and Countering the Financing of Terrorism Act. That law requires banks not only to know who their customer is, but also what a usual transaction pattern is, so that deviations from it can be noticed. This is also why this question often appears together with a question about at which banks the enterprise maintains accounts : the bank wants the overall picture of your payment traffic, not just the part that runs through it.