Quick answer: The Additional Information Form has been mandatory for every R&D tax credit claim submitted since 8 August 2023. It must be filed via the Government Gateway before or alongside the amended tax return, describing up to 10 qualifying projects covering at least 50% of qualifying expenditure. Claims filed without it are rejected outright.
What Is the AIF and Why Did HMRC Introduce It?
The Additional Information Form (AIF) is an online form submitted through HMRC's Government Gateway. It was introduced under Regulation 3 of the Research and Development (Prescribed Information) Regulations 2023, made under powers in the Finance (No. 2) Act 2023. The requirement applies to any R&D claim submitted on or after 8 August 2023, regardless of the accounting period to which the claim relates.
HMRC's rationale for introducing the AIF was the scale of non-compliant claims in the R&D tax credits system. HMRC estimated that error and fraud in the system cost approximately £1.13 billion in the 2021 to 2022 tax year, representing around 14.6% of the total R&D relief paid out. The majority of this loss was attributed to claims prepared by unscrupulous advisers for companies that had no qualifying activities, or that had significantly overstated qualifying expenditure.
The AIF shifts the information burden earlier in the process. Previously, HMRC received the amended CT600 and might subsequently open a compliance enquiry. Now, structured information about the claim must be provided before HMRC processes and pays it. This gives HMRC a basis to review the substance of the claim rather than simply the quantum. If you have not yet estimated your claim value, use our free eligibility calculator before working through the AIF requirements below.
Who Must Submit the AIF
Every company making an R&D tax credits claim, under any scheme, for any accounting period, where the claim is submitted on or after 8 August 2023, must submit the AIF. There are no exceptions.
This includes:
- Companies claiming under the merged RDEC scheme (from April 2024)
- Companies claiming under ERIS
- Companies with accounting periods straddling April 2024 that have components assessed under the old SME rules
- Companies amending returns for old periods that were previously filed without a claim
- Companies that have claimed before and are filing their annual claim as usual
The requirement applies to the submission date, not the period date. A company filing a first-time claim for a period ending in March 2022, submitted in 2024, must submit the AIF even though the period predates the AIF requirement.
If your accounting period begins on or after 1 April 2023 and you are either claiming R&D tax relief for the first time or have not made a claim in the previous three years, you must also submit a claim notification form to HMRC. This is a separate, earlier requirement from the AIF: it must be filed within six months of the end of the relevant accounting period, and missing this deadline forfeits the right to claim for that period with no appeal route. The claim notification form is not the same as the AIF; both forms must be filed. See the R&D year-end deadlines guide for how the six-month notification window interacts with the two-year claim window.
What the AIF Requires: Section by Section
| Section | What HMRC Asks | Tips for Completing |
|---|---|---|
| Company and claim details | UTR, accounting period start and end dates, total qualifying R&D expenditure, scheme (merged / ERIS) | Confirm the UTR matches the CT600 exactly. Dates must match the accounting period, not the tax year. |
| SIC code and VAT registration number | Standard Industrial Classification (SIC) code as registered at Companies House; VAT registration number if the company is VAT-registered | Use the SIC code currently filed at Companies House for the claimant entity, not a parent or holding company code. If the claimant is not VAT-registered, leave the VAT field blank rather than entering a group VAT number. |
| Connected company details (ERIS claimants only) | For companies claiming under Enhanced R&D Intensive Support (ERIS): the total relevant costs and qualifying R&D expenditure of each connected company in the period, enabling HMRC to verify the 40% R&D intensity condition | A connected company is a 51% group company under the Corporation Tax Act 2010. The intensity condition is assessed against consolidated group costs, not the claimant company in isolation. Prepare consolidated cost schedules before completing this section of the AIF. |
| Cost breakdown by category | Qualifying expenditure split across: staff costs, externally provided workers, subcontractor costs, consumables, software, data costs, cloud computing costs | Figures must be consistent with the cost schedule used in the CT600. Staff costs should include employer NIC and pension contributions apportioned for qualifying time. |
| Responsible officer | Name, job title, and contact details of the person at the company responsible for the claim | This should be a director or senior finance officer. This person bears accountability for the claim accuracy. They should have reviewed and approved the project descriptions before submission. |
| Adviser details | If an adviser was involved in preparing the claim: their name, company, contact details, and agent reference number | HMRC uses this to track adviser patterns across multiple clients. Using a registered, reputable adviser is relevant here. |
| Project descriptions | For each qualifying project (up to 10, covering at least 50% of qualifying spend): advance sought, scientific or technological uncertainty, approach taken | This is the substantive section. Vague descriptions are the primary trigger for HMRC enquiries. See section below for exactly what HMRC wants. |
The Project Description: HMRC's Most Important Section
The project description section is where most AIF errors occur and where most compliance risks lie. HMRC uses these descriptions to assess whether the claimed activities genuinely meet the statutory definition of R&D: an advance in science or technology achieved by resolving scientific or technological uncertainty.
How many project descriptions the AIF requires
The number of project descriptions required depends on how many qualifying projects the company undertook during the period:
| Qualifying projects in the period | Descriptions required | Expenditure rule |
|---|---|---|
| 1 to 3 projects | All of them | No expenditure threshold applies; every qualifying project must be described |
| 4 to 10 projects | At least 3 | The projects described must together account for at least 50% of total qualifying expenditure for the period |
| 11 or more projects | At least 3, no more than 10 | Together they must cover at least 50% of qualifying expenditure; where reaching 50% would require more than 10 projects, describe the 10 with the highest qualifying expenditure |
Companies with more than 10 qualifying projects should rank them by expenditure and describe from the largest downward until the 50% threshold is reached, subject to the 10-project cap. If the top 10 projects by expenditure account for less than 50% of total qualifying expenditure, describing those 10 nonetheless satisfies the rule.
- The advance sought. What improvement in overall knowledge or capability in a field of science or technology did the project aim to achieve? This must be described at the level of the underlying science or technology, not the commercial application. "We wanted to build a faster reporting tool" is not sufficient. "We sought to develop a real-time aggregation engine capable of processing 50 million records per second with deterministic latency bounds, an advance not achievable with existing distributed systems architectures" is closer to what HMRC requires.
- The baseline state of knowledge. What was already known or publicly available at the start of the project? A competent professional in the field should not have been able to derive the solution from existing knowledge. The project description should demonstrate awareness of that baseline.
- The scientific or technological uncertainty. What specifically was not known at the outset? Where did the uncertainty lie? The uncertainty must be in the science or technology, not in the commercial viability of the project.
- How the uncertainty was addressed. What approaches did the team try? What worked, what did not? The systematic investigation element of R&D is important: it is not sufficient to have achieved a result; HMRC wants to see that the process involved genuine experimentation.
A project description for the AIF typically runs to three to five paragraphs for each qualifying project. It should be written by or with the technical team that worked on the project, not drafted by the finance director alone. The financial aspects of the claim are the finance director's domain; the technical narrative requires input from the engineers, scientists, or developers who did the work.
Qualifying Direct Activities and Qualifying Indirect Activities
The AIF requires companies to report qualifying expenditure disaggregated by whether staff time relates to Qualifying Direct Activities (QDA) or Qualifying Indirect Activities (QIA). Both categories attract relief, but the distinction is important for the AIF: a claim that allocates an implausible proportion of staff costs to QDA (for example, 100% of all technical headcount with no QIA element) is a recognised enquiry trigger.
Qualifying Direct Activities
QDA are activities that directly contribute to resolving a scientific or technological uncertainty. HMRC's guidelines identify four types:
- Work that directly attempts to resolve an element of the scientific or technological uncertainty associated with the advance sought
- Creating or adapting software, materials, or equipment used solely to resolve that uncertainty
- Scientific or technological planning carried out in direct support of the qualifying project
- Scientific or technological design, testing, and analysis directed at overcoming the uncertainty
The test is whether the activity directly contributes to resolving the uncertainty. A software engineer writing experimental code to test an unproven hypothesis is performing QDA. The same engineer deploying tested, stable code to a production environment is not.
Qualifying Indirect Activities
QIA are activities that support qualifying R&D projects without themselves advancing the science or technology. HMRC's defined QIA categories include:
- Clerical and administrative support provided directly to R&D workers (for example, maintaining project logs, organising research team travel)
- Maintenance of R&D facilities and equipment used in qualifying projects
- HR and recruitment activities carried out specifically to staff qualifying R&D projects
- Training required to enable staff to undertake qualifying R&D activities
- Feasibility studies to determine the scientific or technological direction of a qualifying project
General corporate overhead is excluded entirely from both QDA and QIA. Finance, marketing, and senior management time not directly overseeing R&D projects does not qualify under either category and should not appear in the AIF cost breakdown at all.
Common misclassifications on the AIF
| Activity | Often claimed as | Correct classification |
|---|---|---|
| Project manager coordinating an R&D team but not personally resolving technical uncertainty | QDA | QIA (administration directly supporting R&D workers) |
| IT support maintaining R&D servers and build infrastructure | QDA | QIA (maintenance of R&D facilities) |
| Software engineer writing experimental code to test an unproven hypothesis | QIA | QDA (directly resolving technological uncertainty) |
| Finance team preparing R&D cost schedules and claim workings | QIA | Neither; general finance overhead is excluded entirely |
| Scientist attending a conference related to the project field | QDA | QIA at most, and only where the conference directly and specifically supports a named qualifying project |
The Cost Summary: Getting the Numbers Right
The cost breakdown in the AIF must reconcile precisely with the figures in the CT600. The categories used in the AIF are the statutory qualifying expenditure categories under the merged scheme: staff costs, externally provided workers (agency staff), subcontractor costs, consumables, software, data licence costs, and cloud computing costs.
Staff costs must be apportioned for qualifying time. If an engineer spends 70% of their time on qualifying R&D, only 70% of their salary, employer NIC, and pension contributions are eligible. The apportionment methodology must be defensible: ideally, timesheets or a documented time allocation exercise support it.
For subcontractors, the merged scheme applies a 65% cap on payments to unconnected parties. Only 65% of the gross payment to an unconnected subcontractor is eligible, regardless of the actual cost. Connected party subcontractor costs are eligible in full but are limited to the lower of the actual payment and the cost to the connected party of performing the work.
Overseas subcontractor costs are excluded from the merged scheme except in narrow circumstances. The AIF cost summary must reflect only eligible UK-based subcontractor expenditure, or the narrow qualifying overseas exception where it applies.
Common AIF Errors That Trigger Enquiries
- Vague project descriptions. Descriptions that describe the commercial objective rather than the technical advance, or that use generic language without specific detail about the uncertainty encountered and the approach taken to resolve it. HMRC caseworkers are trained to distinguish between genuine technical uncertainty and commercial novelty.
- Overclaiming staff time. Claiming 100% of all technical staff time as qualifying, without reference to actual qualifying activities or time records. HMRC expects to see apportionment that reflects the reality of how engineers split their time between qualifying R&D and non-qualifying activities (maintenance, bug fixing, routine development, client work).
- Missing the overseas subcontractor restriction. Including overseas subcontractor costs without meeting the narrow exception criteria. This is one of the most common errors in the post-April 2024 merged scheme era, particularly for companies that previously claimed overseas development costs under the old SME scheme.
- Inconsistency between AIF figures and CT600. Cost totals in the AIF that do not match the figures in the amended CT600. This immediately flags a quality problem and invites closer scrutiny of the entire claim.
- No responsible officer review. Project descriptions that have clearly not been reviewed by anyone with technical knowledge of the projects. HMRC notices when descriptions are generic, inconsistent with the company's sector, or contain technical inaccuracies.
In May 2025, HMRC confirmed to agents that claims will no longer be automatically rejected solely because the AIF contains a minor error in the company's UTR or accounting-period dates that prevents HMRC's systems matching the AIF to the corresponding CT600. Where claims had previously been rejected on this basis, HMRC said it would review those cases and take corrective action where appropriate representations had been made. This change applies only to these specific technical matching fields. Material omissions in project descriptions, substantive cost-schedule discrepancies, and other accuracy failures remain full enquiry triggers and are unaffected by the update.
Timing: Submit AIF Before CT600
The correct sequence for submitting an R&D claim under the current rules is as follows.
- Prepare the AIF - Complete all sections, including project descriptions reviewed and approved by a responsible officer. Agree the cost schedule with the finance team.
- Submit the AIF via Government Gateway - The form is submitted online through the company's HMRC Government Gateway account. A submission reference is generated. Note this reference; it is needed for the CT600.
- Prepare the amended CT600 - Include the R&D claim figures in the appropriate boxes. The CT600 figures must match the AIF cost breakdown exactly.
- Submit the amended CT600 - The amended corporation tax return is filed by the company's accountant or the authorised R&D specialist. HMRC's systems link the AIF submission to the CT600 using the company's UTR and accounting period dates.
- HMRC processing - HMRC reviews the AIF and CT600 together. Standard processing time is 40 working days. HMRC may request further information; a well-prepared AIF minimises this risk.
- Payment or tax credit applied - For loss-making companies, a cash payment is issued. For profitable companies, the corporation tax liability is reduced.
The critical constraint is that the AIF must precede the CT600. HMRC cannot match an amended return to an AIF that does not yet exist on their systems. Submitting the CT600 first and the AIF second results in the claim not being recognised.
Working With a Specialist Versus Completing the AIF Yourself
Some finance directors ask whether they can complete the AIF without specialist help. For simple claims with straightforward qualifying activities and good existing documentation, it is possible. For most companies, the benefit of working with a specialist outweighs the cost significantly.
A specialist adds value at two points in the AIF process. First, in identifying and articulating the qualifying activities correctly: a specialist with experience across multiple companies in your sector knows how HMRC evaluates project descriptions and can write them in a way that demonstrates the R&D test is met, rather than leaving it to HMRC to infer. Second, in constructing the cost schedule: apportioning staff time, applying the 65% subcontractor cap, identifying eligible software and cloud costs, and excluding overseas subcontractor costs correctly all require familiarity with the rules that most finance directors do not have.
The risk of an incorrectly prepared AIF is not just a rejected claim. An AIF that triggers an HMRC compliance enquiry creates a significant time and cost burden, even if the underlying claim is legitimate. The cost of getting the AIF right in the first place is almost always less than the cost of dealing with an enquiry.
Uplift Tax introduces companies to HMRC-registered specialists who prepare the AIF as part of the full claim service. The project descriptions are written with your technical team and reviewed by a responsible officer before submission. The cost schedule is reconciled to the CT600. The entire process is managed to the filing deadline.