The essential guide to the R&D Additional Information Form

The Additional Information Form (AIF) is a must for any small UK business that prepares Research and Development (R&D) tax relief.

If your business is making a Research and Development (R&D) tax claim, the Additional Information Form (AIF) is now one of the most important elements of HM Revenue & Customs (HMRC) compliance. Since its introduction in August 2023, the AIF has fundamentally changed how companies justify their R&D tax relief.

HMRC now expects clearer, more structured explanations of what R&D work was carried out, how it meets the definition of R&D, and how qualifying expenditure has been calculated. Failing to meet these expectations can result in delayed repayments, rejected claims, or increased scrutiny.

This guide explains everything you need to know about the Additional Information Form (AIF), how it supports your R&D tax relief claim, and how to stay fully compliant with HMRC’s latest requirements.

What Is the Additional Information Form (AIF)?

The Additional Information Form (AIF) is a mandatory online submission that supports every R&D tax claim submitted to HMRC. It was introduced by HMRC as part of wider reforms to improve R&D tax relief compliance and reduce error and fraud.

The AIF provides HMRC with structured information that explains:

• Who is making the R&D tax claim?
• What R&D activities were undertaken
• How qualifying R&D expenditure was calculated
• Why the work qualifies for R&D tax relief

Key compliance point:
The AIF is a standalone online submission, not attached to the CT600. Claims without a completed AIF are automatically rejected.

You must submit the AIF before filing your Corporation Tax Return and confirm submission by ticking Box 657 on the CT600.

Who must submit an AIF for an R&D tax claim?

Every UK company claiming R&D tax relief must submit an Additional Information Form, regardless of the scheme used (merged R&D scheme or ERIS). There are no exemptions. If your accounting period ends on or after 8 August 2023, an AIF is required as part of your R&D claim submission.

What information is required for HMRC compliance?

The AIF is designed to standardise how information is presented to HMRC. Each section plays a specific role in demonstrating that your R&D tax claim is accurate, eligible, and supported by evidence.

Company information

This section establishes the claimant’s identity and ensures HMRC can correctly match the AIF to your Corporation Tax Return. Any inconsistencies here can delay processing or trigger follow-up queries. The information required is:

• Business name
• Corporation Tax UTR
• Employer PAYE reference
• VAT number – where the business is VAT registered

R&D claim contacts

HMRC requires clear visibility over who is responsible for the claim. This allows them to:

• Direct technical or financial questions efficiently
• Understand whether an external agent was involved.
• Assess accountability and governance.

Accounting period

The accounting period must exactly match the CT600. Even minor discrepancies can result in your R&D claim being rejected and needing resubmission.

R&D intensity and financial data

This section supports HMRC’s assessment of:

• Whether enhanced relief rates (ERIS) apply
• Whether loss-making and intensity thresholds are met
• How R&D spending compares to overall company expenditure.

For newer accounting periods, this is a high-risk area for compliance errors. Often, newly formed companies have a longer than twelve-month first accounting period, which can result in a mismatch when submitting the Additional Information Form (AIF)

Qualifying Activities for an R&D tax Claim

Understanding and accurately describing qualifying activities is critical to compliance when submitting your R&D tax relief.

Qualifying R&D expenditure breakdown

Here, HMRC expects a clear, logical breakdown of qualifying costs. The aim is to show:

• That costs are directly linked to R&D activity.
• That expenditure has been categorised correctly.
• That no ineligible costs have been included

Poor cost categorisation is one of the most common reasons for HMRC enquiry

Qualifying Direct Activities (QDA)

Qualifying Direct Activities are those that directly contribute to achieving a scientific or technological advance. HMRC uses this information to assess whether your work genuinely meets the definition of R&D.

These activities typically involve:

• Resolving technical uncertainty
• Developing or improving products, processes, or services
• Applying scientific or technological principles in new ways

HMRC expects these activities to be clearly linked to named projects.

Qualifying Indirect Activities (QIA)

Qualifying Indirect Activities support R&D projects but do not, in themselves, create the advance. While allowable, HMRC closely scrutinises QIA to ensure:

• Activities are genuinely in support of R&D
• Costs are proportionate
• Non-R&D overheads are not being included.

Incorrectly classifying QIA often triggers HMRC compliance checks.

R&D project description

Project descriptions are the technical backbone of your R&D tax claim. HMRC uses these to decide whether your activities genuinely qualify for relief.

Each project description should include:

• Project Name
• The main field of science or technology to which the project relates
• What existing scientific or technological knowledge did it plan to improve
• What advancement in scientific or technological knowledge the project aimed to achieve
• What scientific or technological uncertainties faced
• How the project sought to overcome those scientific or technological uncertainties

You will need to make sure there is a detailed description of your project. Generic or high-level descriptions significantly increase the risk of enquiries, particularly for high-value claims.

How many project descriptions are required?

HMRC recognises that businesses vary widely in how they structure R&D. The AIF therefore applies a proportionality approach to project descriptions.

If the company has more than one R&D project, HMRC requires specific details depending on the number of projects.

• If claiming for 1 to 3 projects, each project needs to be described separately.
• If claiming for 4 to 10 projects, the company must choose at least 3 projects to describe. These projects must account for at least half of the total R&D costs.
• If claiming more than 10 projects, the company must select at least 3 to describe. These projects must account for at least half of the total R&D costs.

The goal is to give HMRC enough technical detail to understand:

• Where the majority of R&D expenditure sits
• What types of uncertainty are being solved
• Whether the claim aligns with the scale of activity

Failing to describe enough projects or choosing the wrong ones can weaken the credibility of your R&D tax claim.

Do you still need an R&D claim report?

Yes. While the AIF is mandatory, it does not replace a detailed R&D claim report.

The AIF captures structured data. A claim report provides:

• Technical depth
• Narrative explanation
• Context around complex projects
• Supporting evidence

Submitting both together creates a much stronger HMRC compliance position and reduces the likelihood of follow-up questions.

Common AIF and R&D claim mistakes

Many rejected or delayed claims fail for avoidable reasons, including:

• Inconsistent figures between the AIF and CT600
• Overly vague or repetitive project descriptions
• Weak explanations of technical uncertainty
• Incorrect activity or cost classification
• Late submission of the R&D Claim Notification Form (for accounting periods starting on or after 1 April 2023)

Each of these issues increases the risk that HMRC will reject the R&D claim.

Expert Support for R&D Tax Relief Claims

Navigating the AIF alongside wider merged R&D tax relief rules can be complex, especially as HMRC scrutiny increases.

Many UK businesses trust R&D tax experts to deliver compliant, enquiry-resistant R&D tax claims, including:

• AIF preparation and submission
• Technical project documentation
• Financial reconciliation
• HMRC ready reporting

Book a call to ensure your next R&D tax claim is robust, compliant, and optimised for success.

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