The HMRC R&D Additional Information Form is a mandatory digital submission you file through HMRC’s online service before, or on the same day as, your Corporation Tax Return. It captures your project descriptions, cost breakdown, and contact details in a standardised format, and if it is missing when the CT600 arrives HMRC removes the R&D claim from your return automatically, with no enquiry and no chance to explain. The form applies to claims under the legacy SME scheme, the legacy RDEC, the merged RDEC scheme for accounting periods beginning on or after 1 April 2024, and Enhanced R&D Intensive Support (ERIS).
What to Have Ready Before You Sign In
Access is through tax.service.gov.uk. Company representatives sign in with the Government Gateway user ID and password used when registering for Corporation Tax. Agents must sign in through their agent services account first; without that step you cannot open the form. If you have never used Government Gateway, you can create a user ID the first time you sign in.
Each company in a group needs its own Government Gateway account. A “Group Tax Manager” account cannot be used to file for multiple entities.
Before you open the form, translate your internal project notes into the categories the form expects: the technical advance sought, the uncertainties faced, and the systematic work done to resolve them. Doing this outside the portal saves significant time.
Do You Need to File a Claim Notification First
The Additional Information Form is not always the first step. A separate claim notification form is required if you are claiming R&D relief for the first time, or if your last accepted claim was made more than three years before the end of your claim notification period. That period starts on the first day of your period of account and ends six months after the last day of that period. Miss the notification deadline and the entire R&D claim is invalid, no matter how well you complete the Additional Information Form afterwards.
You do not need to notify if you have already made an accepted R&D claim within the three years ending on the last date of your claim notification period. Two situations override that exemption. If HMRC previously rejected a claim by removing it from a return, that earlier claim does not count. Nor does a claim for an accounting period beginning before 1 April 2023 that was filed via an amended return received on or after 1 April 2023. In either case, you must notify again.
Company and Contact Details
The form asks for your company’s ten-digit Unique Taxpayer Reference. It must exactly match the UTR on your CT600. It also asks for the start and end dates of the accounting period, and these must match the CT600 to the day. A mismatch of a single day causes HMRC to reject the form and remove the R&D claim.
Companies registered in Northern Ireland must also give their Company Registration Number and registered business address from Companies House. Companies registered in England, Scotland, or Wales are not asked for a CRN.
You must name the main senior internal R&D contact responsible for the claim, typically a company director, with their contact details. You must also disclose every external agent who helped with the claim. That includes agents who advised on costs, prepared technical assessments, completed the form, or worked on the CT600 itself.
How Many Projects to Describe
The number of projects you describe depends on how many you are claiming for.
- For 1 to 3 projects, describe every project.
- For 4 to 10 projects, select at least 3 projects that together account for at least half of your total qualifying expenditure, and describe those.
- For more than 10 projects, the same 50% rule applies, but if you would need more than 10 to reach the threshold, describe the 10 with the highest qualifying spend.
If you are claiming under both a tax relief scheme and an expenditure credit scheme in the same period, you provide project details separately for each, and the 50% threshold applies independently to each scheme’s qualifying costs.
The Three Technical Descriptions
For each project you describe, the form asks for three pieces of technical narrative. This is where most claims stand or fall under HMRC scrutiny.
The first asks what scientific or technological advance the project aimed to achieve. Focus on the underlying science or technology, not the product or service. Explain how the project intended to extend knowledge or capability beyond what was already known or achievable in the field when the work began. Saying you built a faster app is not enough; you have to explain what technical barrier made “faster” hard.
The second asks what scientific or technological uncertainties the project faced. Describe why the solution was not obvious to a competent professional in the field. HMRC defines a competent professional narrowly: someone with high-level qualifications and continuous professional development, significant years of experience at a senior level, or a strong publication or recognition record in the relevant discipline. Working in the field or having a general interest is not enough. The uncertainty must be technical. Commercial risk, tight deadlines, and budget constraints do not count.
The third asks how you sought to overcome those uncertainties through systematic investigation. Describe the testing, analysis, prototyping, or experimentation carried out during the accounting period. HMRC expects a clear line from uncertainty to method to outcome, or to ongoing work if the project has not concluded.
Breaking Down Qualifying Expenditure
The form requires costs split into specific qualifying categories. The exact categories depend on the scheme, but the core cost types are the same.
Staffing Costs
Qualifying staffing costs include gross salaries, employer Class 1 National Insurance contributions, and employer pension contributions for directors and employees directly engaged in R&D. If someone splits time between R&D and other work, only the proportion spent on qualifying activities is claimable. HMRC allows the same apportionment for holiday pay and sick pay as for working time, treating them as a necessary cost of employing the person.
Director dividends do not qualify. They fall outside the statutory definition of staffing costs. Where a director takes a low salary supplemented by dividends, only the salary portion, apportioned for R&D time, is eligible. Benefits in kind are also excluded.
Externally Provided Workers
Costs for agency staff and other externally provided workers sit in a separate category from staffing costs. Under the merged RDEC scheme and ERIS, 65% of the payment to an unconnected EPW qualifies, but only where the worker is subject to UK PAYE. Overseas EPWs and those not taxed through PAYE are excluded, even if they would have qualified under the legacy rules.
Subcontractor Costs
The qualifying amount for subcontracted R&D depends on whether the subcontractor is connected to your company. For unconnected subcontractors, 65% of the payment qualifies. For connected subcontractors, the qualifying amount is capped at the lower of the payment you made or the subcontractor’s own relevant R&D expenditure, meaning their staffing, software, data, and consumable costs, excluding anything they subcontracted out.
Software, Consumables, Cloud Computing, and Data Licences
Software licences and consumable items used or transformed during R&D are claimable. For accounting periods beginning on or after 1 April 2023, cloud computing services and data licence costs also qualify, but only to the extent they directly contribute to resolving a scientific or technological uncertainty. Costs tied to qualifying indirect activities, meaning support work that does not itself resolve the uncertainty, do not qualify in these categories.
HMRC accepts reasonable apportionment where services are used for both R&D and non-R&D purposes. Acceptable methods include apportioning by staff hours on qualifying activities, by number of licences used, or by the ratio of data storage devoted to R&D. Keep records of access, duration, and purpose to support the split.
Two exclusions catch companies out. Data licence costs do not qualify if your company has a contractual right to sell the data onward, unless your transformation is significant enough that the original inputs can no longer be identified. Costs also do not qualify if you have a right to publish, share, or otherwise communicate the data to third parties, though sharing that is reasonably necessary for the R&D itself, including intra-group communications or peer-reviewed publication, is permitted.
Submitting the Form in the Right Order
Timing is the single most common procedural failure. The Additional Information Form must be submitted before or on the same day as the CT600. If you submit both on the same day, the form must go first. If the CT600 arrives even moments before the form, HMRC rejects the R&D claim.
Once you complete every field and confirm the declaration that the information is accurate, the portal generates a unique submission reference number. Keep it. That reference is your primary proof that you met the statutory requirement. The system also sends an automated confirmation email to the registered contact address.
If you later amend your R&D claim on the CT600, submit a new Additional Information Form to support the amended figures. The same timing rule applies to the amendment: new form first, or same day, never after.
What Happens If You Get It Wrong
If the form is missing when the CT600 arrives, HMRC writes to confirm that the R&D claim is being removed from your return. There is no enquiry and no opportunity to explain. The claim is invalid under the Finance (No. 2) Act 2023. If the removal happens close to the deadline for amending the return, you may not have time to resubmit and could lose the claim for that accounting period entirely.
Even when the form is submitted on time, HMRC uses it to risk-score claims. Mismatched accounting period dates, cost figures that do not reconcile with the CT600, or vague technical narratives can trigger a compliance check. Keep internal records that mirror everything you entered, because HMRC may request supporting evidence at any point after submission.
Which Scheme Applies to Your Claim
The scheme changes which cost categories the form asks about, so identify it before you start entering figures. For accounting periods beginning on or after 1 April 2024, most companies use the merged RDEC scheme. Loss-making SMEs whose qualifying R&D expenditure is at least 30% of their total expenditure may instead claim under Enhanced R&D Intensive Support. The legacy SME scheme and legacy RDEC still apply to accounting periods beginning before 1 April 2024; a late or amended claim for an earlier period will ask you to identify the relevant legacy scheme.