Your advisor charges 20%? It costs you 26.
French tax law removes success-based advisory fees from the R&D tax credit base. You pay twice: the fee, then the credit that fee destroys. On a flat fee under €15,000, nothing happens.
The text, so you can check
Article 244 quater B, III of the French tax code: advisory costs incurred to obtain the credit are deducted from the base — entirely when fees are set as a share of the credit, and for other fees, only above the higher of €15,000 excl. VAT or 5% of eligible spend net of public grants.
This comparator applies that rule and nothing else. It does not say which advisor to pick: an expensive one who secures a contested file beats a cheap one who leaves you alone in an audit.