The R&D Tax Credit SME Definition requires that a company must have less than 500 staff, and less than either of 100m Euros turnover or 86m Euros of assets.
However, this is assessed on a group-wide basis as per the EU definition described here. This is always something that we look at on a per-client basis before making a claim, but in very broad terms, what this means is that if the company has more than 25% ownership in, or is owned by another company, then you have to include their figures in the calculation, as well as any holdings at a similar level that they in turn may have. Furthermore, companies can be linked through individual shareholders if they have control of other companies in an upstream or downstream enterprise (i.e. they supply or receive goods or services from the claimant company). Note that if the holding is between 25% and 50%, it may be a pro-rata aggregation rather than the entirety.
There is a useful calculator tool developed as a collaboration between the European Commission, the Walloon Union of Enterprises, Belgium and the agency for administrative simplification in Wallonia, Belgium. Note that this is not provided by us and no responsibility is taken for the result of it.
This tool will let you calculate if you are an SME for R&D tax relief purposes.