7 April 2026
3 min read
Patent Box claims have often been treated as a figures-only exercise. HMRC’s GfC9 guidance makes clear that supporting calculations and explanations are now expected alongside the tax computation.
For a long time, Patent Box claims were often treated as a figure-only exercise. If the calculation was correct and included in the tax computation, that was usually considered enough. Nowadays, Patent Box can no longer be treated as a simple line in the tax computation. HMRC now expects clear supporting information to sit behind the numbers and explain how the claim has been prepared.
From “just figures” to fully documented claims
The Patent Box regime has changed significantly since its introduction in 2013, particularly with the introduction of the nexus rules (which require companies to show a clear link between their own qualifying R&D activity and the profits they are claiming at the 10% rate).
More recently, HMRC’s Guidance for Compliance (GfC9), published in November 2024, set out what it sees as good practice in making Patent Box claims: HMRC now expects claims to be supported by clear calculations and a narrative that explains how those figures have been reached.
While GfC9 sets a high bar for “best practice,” following it is not a legal obligation in the sense that a claim without a narrative is technically valid under law. However, HMRC has stated that claims lacking this supporting information are significantly more likely to trigger a compliance check or formal inquiry.
What your supporting information should cover
GfC9 strongly encourages companies to send supporting details with the tax return that contains the Patent Box claim. HMRC is looking for a clear, traceable story behind the claim.
HMRC wants to see:
What this means for claimants
GfC9 clarifies HMRC’s expectations. For companies already within Patent Box, this is about process and documentation rather than brand new rules. You need to be able to show, in a simple narrative, how your patents, income and R&D link together and how that feeds into the final 10% rate. Done well, this reduces the chances of HMRC asking for extra information later and makes any questions easier to deal with if they do arise.
ABGi has always prepared Patent Box claims in an evidence led way, with detailed technical and financial analysis and supporting reports that clearly explain the link between R&D, IP, and profit, in the way that GfC9 describes as good practice. Our technical consultants work directly with engineers and technical staff, and are able to translate that activity into the kind of clear, evidence-led narrative HMRC is now expecting.
If you have any questions about Patent Box or IP Planning, please contact the ABGi Team. We’ll get back to you to discuss your unique needs and explain how we can assist.