HMRC’s R&D Additional Information Form: what it means for your claim

‍What the Additional Information Form (AIF) is and why HMRC introduced it

The AIF is an online form that supports an R&D claim by asking for structured information about your company, your projects and your costs. HMRC introduced it to standardise what gets submitted and strengthen upfront checks, so claims can be assessed with more consistency and less guesswork.  

In simple terms, the AIF is HMRC saying: “Show us what you did, why it qualifies and how the numbers were built.”

The admin detail that can make or break a claim

If you submit your CT600 before the AIF, HMRC can reject the R&D claim. The AIF must be submitted before, or on the same day as, the Company Tax Return. If both are filed on the same day, the AIF must be submitted first.  

That is why AIF is not just a form. It is a submission gate.

What HMRC is really looking for

AIF is not asking you to write an essay. It is asking you to be specific and consistent. The strongest submissions tend to have three qualities.

1) A clear technical story

HMRC is trying to understand whether your work meets the R&D definition for tax purposes. That means explaining:

• What advance you were trying to achieve in science or technology
• What was uncertain and why it was not readily solvable by a competent professional
• What you did to resolve the uncertainty, such as trials, prototyping, testing, or systematic development  

Generic statements like “we improved the product” rarely help. Plain, technical explanations do.

2) Costs that map cleanly to the projects

AIF makes it harder to hide messy cost builds. If staff time, contractor spend, or software and cloud costs are included, HMRC will expect the numbers to be traceable back to evidence and apportioned on a reasonable basis. The cost categories and rules are set out in HMRC guidance, and it is worth aligning your internal tracking to those categories early.

3) A sensible project selection approach

You do not always have to describe every project, but you do need to follow HMRC’s selection rules. For claims with multiple projects, you must describe a minimum number and ensure the projects described cover a required share of qualifying spend.  

If your project list is long, good selection becomes part of claim strategy. Choose projects that are both high spend and easy to evidence.

How AIF fits with the merged scheme and ERIS

For accounting periods beginning on or after 1 April 2024, the UK moved to the merged R&D tax relief scheme, with Enhanced R&D Intensive Support (ERIS) available for eligible loss-making R&D-intensive SMEs.  

AIF sits alongside these schemes. It does not change what is eligible on its own, but it raises the standard of what you need to present upfront.

Two knock-on effects matter in practice:

• Claims need earlier input from technical teams. Finance can no longer “fill in the gaps” at the end of the year without risking weak narratives and mismatched costs.
• Process and deadlines matter more. Missing admin steps can block a claim even when the underlying R&D is genuine.

Claim notification is separate, and it catches first-timers

AIF is not the only process step. Depending on your claim history, you may also need to submit a Claim Notification Form (CNF) before you claim. This is required if you are claiming for the first time, or if your last claim was made more than three years before the end of your claim notification period.  

The claim notification period ends six months after the end of your period of account.  

If you are not sure whether it applies, check early. This is not the kind of thing you want to discover during CT600 week.

Common pitfalls we see and how to avoid them

Filing CT600 before AIF

This is the classic avoidable problem. Build a simple rule into your tax return workflow: AIF first, CT600 second.  

Treating AIF as a marketing summary

AIF is not the place for glossy language. Focus on technical uncertainty and what you did to resolve it.  

Weak links between people, activity, and cost

If you cannot show who did the R&D, what they did, and how that maps to the costs claimed, you are building risk into the submission.

Leaving it late

AIF forces collaboration across finance, engineering and leadership. Starting early usually improves quality and reduces rework.

What to do next

If you are preparing an R&D claim:

• Confirm whether claim notification applies to you
• Lock down your project list and select which projects must be described
• Draft project summaries that focus on the technical uncertainties and the work done
• Build the cost breakdown with clear evidence and apportionment logic
• Submit the AIF first, then file the CT600  

For the full step-by-step process and a practical checklist, use our Support Hub guide.