R&D tax relief •4 min read

The Additional Information Form (AIF)

MJ

Matthew Jones ACA CTA

Last reviewed July 2026

The Additional Information Form (AIF) is a mandatory online form that carries the substance of your R&D claim to HMRC: the projects, the costs, the responsible people and the agents involved. It has been required for every R&D claim submitted since 8 August 2023, whatever the scheme, and it must reach HMRC before or with the company tax return (CT600). A claim filed without it is not a valid claim.

What is the Additional Information Form?

It is HMRC’s standard template for the detail behind an R&D claim. Before August 2023, supporting reports arrived in whatever format the claimant or agent chose, and some claims arrived with no supporting detail at all. The AIF ended that: every claim now presents its projects and costs in the same structure, and everyone who worked on the claim is named.

Treat it as the claim itself rather than an administrative wrapper. When HMRC looks at your claim, the AIF is normally the first document read, and the impression it creates shapes everything that follows.

What information does the AIF require?

Four things.

Project descriptions. Each described project must show how the work meets the statutory definition of R&D: an advance in a field of science or technology, sought through the resolution of scientific or technological uncertainty that a competent professional in the field could not readily resolve. The advance must belong to the field, not merely to your company. Our guide to what counts as qualifying R&D sets the definition out in full.

Qualifying costs. The expenditure behind the claim, broken down by category: staffing, externally provided workers, subcontractors, consumables, software, data and cloud computing, and payments to clinical trial volunteers. The figures need to reconcile with the claim in the return; the categories themselves are covered in which costs qualify for R&D tax relief.

The senior internal R&D contact. A named senior person at the claimant company who is connected to the R&D. This should be someone who can genuinely speak to the work, because HMRC’s questions will be directed here.

Every agent. Each agent involved in the claim must be named. Anonymous advisers are no longer possible, which was part of the point: some unregulated agents built businesses on never appearing in the paperwork. HMRC registration for tax advisers who interact with HMRC is now required as well, so the naming requirement has real teeth. It also gives claimants a simple due diligence question: ask any prospective adviser whether they are registered with HMRC and whether their name will appear on your form.

When must the AIF be submitted?

Before or with the CT600, never after. Sequencing is the simplest thing to get wrong: if the return goes in first and the AIF has not been submitted, the claim is defective. Where one adviser prepares the claim and another files the return, someone has to own the sequence. In our engagements that is us: we are registered with HMRC as tax agents and submit both the AIF and the return ourselves, so the sequence does not depend on a handover between advisers.

The requirement applies to every claim, including claims added to earlier returns by amendment. A backdated claim submitted today needs an AIF just as a current-year claim does, and the same sequencing rule applies to the amended return. Companies revisiting older periods should settle the notification position at the same time: the two requirements operate independently, and failing either one is fatal to the claim.

Where do AIFs go wrong?

Five patterns account for most of the failures we see:

  • The CT600 is filed before the AIF, so the claim fails on sequence alone.
  • Project descriptions read as marketing: they describe a product and its commercial promise rather than the advance in the field and the uncertainties resolved.
  • Project boundaries are drawn around whole development programmes, sweeping routine work into the claim alongside the genuine R&D.
  • The cost figures do not reconcile to the return, or apportionments have no visible basis.
  • The named contact cannot speak to the technical detail when HMRC follows up.

Each of these is avoidable, and each is the sort of signal that invites a full HMRC enquiry, which HMRC currently opens on roughly one in six claims.

How do we prepare the AIF?

From the technical work upwards. That means interviews with your competent professionals, project descriptions written against the statutory definition rather than adapted from marketing copy, and cost workings reconciled line by line before anything is submitted. The named senior contact reviews the full draft before it goes to HMRC: follow-up questions land with that person, and the worst time to read your own project descriptions for the first time is during an enquiry. Every claim is prepared by our specialist team and signed off by a chartered adviser, and every AIF we file names us as agent, as the rules require and as we would want anyway: we stand behind our work, and enquiry support is included in every engagement as standard.

The AIF is one of three procedural steps that decide whether a claim exists at all. The others are the claim notification requirement for first-time claimants and the CT600 itself. Which rules apply to your period depends on your accounting dates, covered in which R&D scheme applies to your company.

Talk it through with a chartered adviser

If you want your next AIF prepared by a regulated chartered firm, or a second pair of eyes on one already drafted, get in touch. For the wider claim process, start with our R&D tax relief guide.

Written by Matthew Jones ACA CTA. Last reviewed July 2026.

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