insurer wants to know how many employees we have what number do I provide

The number of employees comes from the Business Register

The figure you provide is usually the number of employees as registered with the Chamber of Commerce. That number is stated on the extract from the Business Register and is expressed in a range or an exact number, depending on how the business has reported it. Insurers usually ask for this figure as an indicator of size and risk, not as an exact FTE count — a rough but verifiable source is therefore usually sufficient.

If you are in doubt between the number on the payroll and the number of FTE (full-time equivalents), choose the definition stated in the question itself. If it is not there, the Business Register figure is the safest choice because it is externally verifiable. This figure is moreover asked for more often than just by insurers: also in the question how many employees the business has sustainability lists often refer to the same source, and sometimes it is combined with a question about the company's annual turnover to determine the size of the business — for example for the classification small, medium or large SME.

Where that comes from: the Business Register Act

The number of employees is one of the data recorded under the Business Register Act 2007 for every business. This is therefore not an estimate or separate declaration that you have to calculate yourself, but an existing, externally registered fact. If you want to substantiate the figure more precisely than the range from the Business Register allows — for example because the insurer asks for a reference date — then the company's own payroll administration is the appropriate source, but that is then a supplement to the Business Register figure, not a replacement for it.